## Converting Epsilon NFA to NFA using Epsilon Closure

Given an Epsilon NFA transition table or transition diagram, task is to convert the $\epsilon$-NFA to NFA.

#### Solution:

Let, E be the name of the $\epsilon$-NFA. The tuple of the epsilon automaton are,

$E = (Q, \sum, \delta, q_0, F) = ( \{ p,q,r \}, \{ a,b,c \}, \delta, p, \{ r \} )$

###### Informal Explanation:

First Task is to find epsilon closure of all the state of the finite automaton. In order to do so take the state and for each outgoing edge with input symbol of epsilon go to that state. From that state keep going to other states the same way following epsilon. Basically it is the states on the path following only epsilon symbol.

Epsilon closure of state is the state itself and any other states that are reachable along the path following only epsilon symbol.

Epsilon closure is identified with ECLOSE(q) for state q. So,

$ECLOSE(p) = \{ p,q,r \} \\ ECLOSE(q) = \{ q \} \\ ECLOSE(r) = \{ r \} \\$

Epsilon closure of p is set {p,q,r} because from p on seeing epsilon the non deterministic finite automaton can stay in the same state. It may also go to q on seeing epsilon. Again r is also in the set because from p on seeing epsilon there is a transition to r. If upon reaching q or r from p, there were epsilon transition the also go to those states and include them in the ECLOSE set of p.

$p \xrightarrow[ ]{ \epsilon } q \\ p \xrightarrow[ ]{ \epsilon } r \\$

In case of epsilon closure of q and r states there are no transitions on epsilon. So their only ECLOSE is singleton set containing that state itself.

## Fibonacci Number Generation with Golden Ratio Code

The formula and explanation are all available in here in wikipedia. It won’t produce correct result for any number greater than 70.

##### Code Fibonacci Generation with Golden ratio:
/**
* Author:    Asif Ahmed
* Site:      https://quickgrid.wordpress.com
* Problem:   Fibonacci number generation using golden ratio.
* Technique:
*/

#include<bits/stdc++.h>
using namespace std;

int main(){

//freopen("input.txt", "r", stdin);
//freopen("output.txt", "w", stdout);

long double phi  = 1.61803398874989484820458683436563811772030917980576286213544862270526046281890;
long double phiN = 0.61803398874989484820458683436563811772030917980576286213544862270526046281890;

// Change value of n to desired value.
// Should give correct Fibonacci value for 1 to 70.
int n = 70;

long double F = ( pow(phi, n) - pow( phiN, n ) ) / sqrt(5);

cout.setf(ios::fixed);
cout << setprecision(0) << round(F) << "\n";

return 0;
}


## UVA Problem 913 – Joana and the Odd Numbers Solution

UVA Problem 913 – Joana and the Odd Numbers Solution:

Click here to go to this problem in uva Online Judge.

Solving Technique:

Todo:
1. Reorganize.
2. check for mistakes.


This problem can be solved in quite a few ways. Brute force won’t work. I have given the brute force code anyway. It will give correct answer from 1 < n < 199999999 but the requirement is 1 < N < 1000000000, which is way way larger.

Another approach is to do mathematical calculation to come up with a formula to solve this. Multiple formula can be generated such as a single formula or, one formula complementing other or, multiple formula's combined. I have provided two formula in the codes below.

One thing to mention, the output or input must be long long data type. Other data types will give incorrect output.

Unfortunately I won’t be elaborate more than this. It took 5 pages to solve this many way with proof, but that’s a lot to write. I will try to explain a way for coming up with these formula.

##### The brute force way:

A simple way to do this is, for values greater than 1 set offset 10 and start multiplying with 5. For each step increase offset by 4 and add value to previous multiplying value.

Input -> Sum

3 -> 3 * 5
5 -> 3 * 15, [ 15 = 5 + 10 ]
7 -> 3 * 29, [ 29 = 15 + 14 ]
9 -> 3 * 47, [ 47 = 29 + 18 ]
11 -> 3 * 69, [ 69 = 47 + 22 ]
13 -> 3 * 95, [ 95 = 69 + 26 ]

Although this approach will not work since the range is huge. It is possible to pre-calculate for a certain range and anything outside that calculate with formula.

##### Trying to Come up with a Closed Form Expression:

First thing is to notice is that the numbers differ by 2 and are odd. So, if the first number is n, then the sum of n and next two numbers is,

$n + ( n + 2 ) + ((n + 2) + 2) = n + n + 2 + n + 4 = 3n + 6$

Ex:
If n was 67, then result of 3n + 6 = 207.

The opposite is also true. For example, given sum of three numbers we can find the first number by,
if sum was 141 then,

$3n + 6 = 141 => n = 45$

Expanding and writing the sequence in format below,

###### Input – Values in the Row(Last three numbers bracketed) – Sum
1 - [ 1 ] - 1
3 - [ 3 5 7 ] - 15
5 - 9 11 [ 13 15 17 ] - 45
7 - 19 21 23 25 [ 27 29 31 ] - 87
9 - 33 35 37 39 41 43 [ 45 47 49 ] - 141
11 - 51 53 55 57 59 61 63 65 [ 67 69 71 ] - 207
13 - 73 75 77 79 81 83 85 87 89 91 [ 93 95 97 ] - 285


This means for a given value there are that many numbers in that row.

##### Trying to come up with a Brute Force Approach:

This is extra and not required to solve this problem but it will understand creation of the formula.

The first numbers of every row can be generated and memoized in a table sequentially using the formula below,
row – number break down – first number

1 -> 1 -> 1
3 -> 1 + ( 1 * 2 ) -> 3
5 -> 3 + ( 3 * 2 ) -> 9
7 -> 9 + ( 5 * 2 ) -> 19
9 -> 19 + ( 7 * 2 ) -> 33

Let n1 be equal to 1 and n2, n3 …, nk be next generated sequences. So the formula is,
n1 = n1
n2 = n1 + (1 * 2)
n3 = n2 + (3 * 2)
n4 = n3 + (5 * 2)
n5 = n4 + (7 * 2)
……………..
……………..
nk = n(k-1) + (i * 2)

this can be converted to an algorithm,
Let, T be table to store value of the first number.
n1 = 1
T[n1] = n1

i = 3

for i to size
T[i] = T[i-2] + (i-2) * 2
increment i by two
End

#### Generating Solution From the Output:

Similarly, The sum can also be calculated in terms of input by creating a sequence and finding out the formula.

1 -> 1
3 -> 15
5 -> 45
7 -> 87
9 -> 141
11 -> 207
13 -> 285

when they are written in a sequence,

1 + 15 + 45 + 87 + 141 + 207 + 285 + …………..

So, for 11 the output should be 207. The formula can be calculated from the picture above

207 = 141 + 66
207 = 141 + (54 + 12)
207 = 141 + ((12 * 5) – 6 + 12)
207 = 141 + ((12 * 6) – 6)
207 = 87 + 54 + ((12 * 6) – 6)
207 = 87 + ((12 * 5) – 6) + ((12 * 6) – 6)
207 = 45 + ((12 * 4) – 6) + ((12 * 5) – 6) + ((12 * 6) – 6)
207 = 15 + ((12 * 3) – 6) + ((12 * 4) – 6) + ((12 * 5) – 6) + ((12 * 6) – 6)
207 = 1 + ((12 * 2 – 6) – 4) + ((12 * 3) – 6) + ((12 * 4) – 6) + ((12 * 5) – 6) + ((12 * 6) – 6)
207 = (12 * 2 – 6) + ((12 * 3) – 6) + ((12 * 4) – 6) + ((12 * 5) – 6) + ((12 * 6) – 6) – 3

this can be written as summation formula,

$-3 + \sum_{i = 2}^{ceil( \frac{n}{2} )} 12i - 6$

this can be rewritten as,
$-3 + 6 * \sum_{i = 2}^{ceil( \frac{n}{2} )} 2i - 1$

The input for this formula is the input for the program,
for, n = 17 the sum of last three numbers should be 477.
Setting n = 17 in following the formula it will give,

-3 + 6 * ( 3 + 5 + 7 + 9 + 11 + 13 + 15 + 17 ) = 477

The formula above doesn’t quite work out for 1. Although we know for 1 output is 1 but it should be included in the formula. Expanding and changing values the summation will get the formula for all values.

Similarly, this is the formula to calculate the first number to sum from a row. It was calculated making a sequence of first summing numbers and find out the the summation formula,

First number,
$N = 3 + 2 * \sum_{i = 2}^{floor( \frac{n}{2} )} 2i + 1$

Separating the summation,
$\sum_{i = 2}^{floor( \frac{n}{2} )} 2i + 1 = 2 * \sum_{i = 2}^{floor( \frac{n}{2} )} i + \sum_{i = 2}^{floor( \frac{n}{2} )} 1$

$= 2 * ( \sum_{i = 1}^{floor( \frac{n}{2} )} i - \sum_{i = 1}^{ 1 } i ) + \sum_{i = 1}^{floor( \frac{n}{2} )} 1 - \sum_{i = 1}^{ 1 } 1$

$= 2 * \sum_{i = 1}^{floor( \frac{n}{2} )} i - 2 + \sum_{i = 1}^{floor( \frac{n}{2} )} 1 - 1$

$= floor( \frac{n}{2} ) ( floor( \frac{n}{2} ) + 1 ) + floor( \frac{n}{2} ) - 3$

I won’t simplify anymore.

Put the value of summation in the equation,
$N = 3 + 2 * \sum_{i = 2}^{floor( \frac{n}{2} )} 2i + 1$
because i only expanded the summation. Multiply result with 2 and add 3 to get the first number.

From, the equation above place the value of first number in 3n + 6 to get the summation of last three numbers for a given number.

The 3n + 6 and the summation formula can be combined into a single formula.

#### Generating Solution based on First Number of Last Three:

Similarly the first number to sum from every row can be calculated. If the first number from every row are written in a sequence,

1 + 3 + 13 + 27 + 45 + 67 + ………………..

The first number can be generated following this,

For input n = 11, task is to generate first number from the graphical representation above. Then the value can be placed in equation, 3N + 6 to generate sum of that value and next two (basically the answer).

67 = 45 + 22
67 = 45 + ( 18 + 4 )
67 = 45 + ( 14 + 4 + 4 )
67 = 45 + ( 10 + 4 + 4 + 4 )
67 = 45 + ( 10 + 4 + 4 + 4 )
67 = 27 + 18 + ( 10 + 4 + 4 + 4 )
67 = 27 + ( 10 + 4 + 4 ) + ( 10 + 4 + 4 + 4 )
67 = 13 + 14 + ( 10 + 4 + 4 ) + ( 10 + 4 + 4 + 4 )
67 = 13 + ( 10 + 4 ) + ( 10 + 4 + 4 ) + ( 10 + 4 + 4 + 4 )
67 = 3 + 10 + ( 10 + 4 ) + ( 10 + 4 + 4 ) + ( 10 + 4 + 4 + 4 )
67 = 3 + 10 + ( 10 + 4 ) + ( 10 + 4 + 4 ) + ( 10 + 4 + 4 + 4 )

this way the formula can be,

$First \ number = 3 + \sum_{i = 1}^{ floor( \frac{n}{2} - 1 ) } 10 + \sum_{i = 1}^{ floor( \frac{n}{2} - 2 ) } 4i$

$First \ number = 3 + 10 * \sum_{i = 1}^{ floor( \frac{n}{2} - 1 ) } 1 + 4 * \sum_{i = 1}^{ floor( \frac{n}{2} - 2 ) } i$

$First \ number = 3 + 10 * ( floor( \frac{n}{2} ) - 1 ) + 2 * ( floor( \frac{n}{2} ) - 2 ) * ( floor( \frac{n}{2} ) - 1 )$

This can be further simplified.

For n = 15 the first number should be 123. Setting n = 15 in equation above,

first number = 3 + 10 * ( 7 – 1 ) + 2 * ( 7 – 2 ) * ( 7 – 1 )
first number = 3 + 60 + 60 = 123

That’s it. There are other approaches but it will take a long time to write.

Important:  Be sure to add or print a new line after each output unless otherwise specified. The outputs should match exactly because sometimes even a space character causes the answer to be marked as wrong answer. Please compile with c++ compiler as some of my codes are in c and some in c++.

More Inputs of This Problem on uDebug.

Input:

3
5
7


Output:

15
45
87


### Formula Generate sequence sum, first number & sum Code:

/**
* Author:    Asif Ahmed
* Site:      https://quickgrid.wordpress.com
* Problem:   UVA 913 Joana and Odd numbers
* Technique: Generate Sequence Sum, First number
*            then generate sum of next numbers
*            including the generated number.
*/

#include<stdio.h>
#include<string.h>

int main(){

//freopen("input.txt", "r", stdin);
//freopen("output.txt", "w", stdout);

long long n;

while( scanf("%lld", &n) == 1 ){

long long m = n >> 1;

long long part = ( (n * (n + 1)) >> 1 ) - ( m * ( m + 1 ) ) - 4;

long long firstNum = 2 * part + 3;

printf("%lld\n", 3 * firstNum + 6);

}

return 0;
}



### Reduced Formula Code:

/**
* Author:    Asif Ahmed
* Site:      https://quickgrid.wordpress.com
* Problem:   UVA 913 Joana and Odd numbers
* Technique: Reduced formula.
*/

#include<stdio.h>
#include<string.h>

int main(){

//freopen("input.txt", "r", stdin);
//freopen("output.txt", "w", stdout);

unsigned long long n;

while( scanf("%lld", &n) == 1 ){

long long ans =  3 * ( (n + 1) * ( n - (n >> 1) ) )  - 9;

printf("%lld\n", ans);
}

return 0;
}



### Brute Force Code( Won’t be Accepted ):


/**
* Author:    Asif Ahmed
* Site:      https://quickgrid.wordpress.com
* Problem:   UVA 913 - Joana and the odd numbers
* Technique: Brute Force. Won't get Accepted.
*            This is just for demonstration. This
*            won't get accepted due to huge size that
*            array can't process. But it will give correct
*            answer till N.
*/

#include<stdio.h>
#include<string.h>

#define N 100000000
//#define M 1000000000

static long long value[N];

int main(){

//freopen("input.txt", "r", stdin);
//freopen("output.txt", "w", stdout);

value[0] = 1;
value[1] = 15;
long long offset = 30;

for( long long i = 2; i < N; ++i ){
value[i] = value[i-1] + offset;
offset = offset + 12;
}

long long n;
while( scanf("%lld", &n) == 1 ){
printf("%lld\n", value[n/2] );
}

return 0;
}


## UVA Problem 10106 – Product Solution (Lattice Multiplication)

UVA Problem 10106 – Product Solution:

Click here to go to this problem in uva Online Judge.

Solving Technique:

This problem is quite simple. Given two very large integers multiply them and print them. By large I mean almost 251 characters long for this problem. So string or character array must be used.

This problem can solved in many ways Big Integer, FFT, Grade School etc. But I have implemented lattice multiplication / Chinese multiplication to solve this problem.

Code Explanation:

The code below requires quite a bit of polish to understand easily ( A lot other post require the same. Maybe I will update this post sometimes in future or not. ).

This code is not quite space efficient. I have used several arrays to make it easy to understand but all of the tasks below can be done using the large array. Also the running time can further be improved to $O(m*n)$ instead of $O(n^2)$. Where, m and n are length of two arrays and they may not be equal in size.

I have provided some graphical representations below to make it easier to understand.

This is an example of how the multiplication works in this code. As mentioned above the process can be sped up using rectangular matrix instead of square if the length is not equal.

This is a representation of how the table / square matrix is filled for further processing.

Multiplication starts with the last character of string 1 and proceeds to first character. For string 2 multiplication starts from the first character till last character. This way each character from string 1 and string 2 is first converted to a digit, then they are multiplied. If the result is two digits it is divided by 10.

The remainder is written as the lower left portion ( indicated by lower in the structure ) and the quotient is written as the upper left portion ( indicated by upper in the structure ).

This is graphical representation of how the structure is traversed. If you have trouble understanding how the recursive function traversing the structure, then take a look at UVA problem 264 – Count the Cantor Solution. The traversal is somewhat similar to that and I have provided explanation int that post.

Rest is explained in the code comments.

Important:  Be sure to add or print a new line after each output unless otherwise specified. The outputs should match exactly because sometimes even a space character causes the answer to be marked as wrong answer. Please compile with c++ compiler as some of my codes are in c and some in c++.

More Inputs of This Problem on uDebug.

Input:

12
12
2
222222222222222222222222


Output:

144
444444444444444444444444


### Code:

/**
* Author:    Asif Ahmed
* Site:      https://quickgrid.wordpress.com
* Problem:   Lattice Multiplication.
* Technique: High precision large number multiplication.
*            Structure array representing upper left and
*            and lower right corner in single cell.
*/

#include<stdio.h>
#include<string.h>

#define M 260

int N;

// Assuming both strings are of same length.
struct multiplicationTable{
int upper;
int lower;
};
struct multiplicationTable node[M][M];

static char string1[M];
static char string2[M];

// stores the diagonal sums;
int sum;

// decides whether to get the upper or lower
// value based on even or odd.
int m;

int recursiveAdder( int i, int j ){

// Termination condition.
if( j < 0 || i >= N )
return sum;

int val;

// Whether to get the upper left corner or
// the lower right corner.
if( m % 2 ){
val = node[i][j].upper;
j = j - 1;
}
else{
val = node[i][j].lower;
i = i + 1;
}
++m;

// store the sum of the whole diagonal.
sum = sum + val;

// recursively visit all row ans column
// diagonally ( at least on pen and paper format ).
// actually moves more like the snake in the snakes game.

return sum;
}

// Debug.
// Print the matrix showing the multiplications.
// Please note left and right directions may be different.
void printMultiplicationMatrix(){

printf("\n\n");
for( int i = 0; i < N; ++i ){
for( int j = N - 1; j >= 0; --j )
printf("%d,%d, ", node[i][j].upper, node[i][j].lower );
printf("\n");
}

}

int main(){

//freopen("input.txt", "r", stdin);
//freopen("output.txt", "w", stdout);

while( gets(string1) ){
gets(string2);

int len1 = strlen(string1);
int len2 = strlen(string2);

// Fix length if both string are not equal size.
// Adding leading zeros to smaller string.
if( len1 > len2 ){
N = len1;

int shiftWidth = len1 - len2;

for( int i = len1 - 1; i >= 0; --i )
string2[i + shiftWidth] = string2[i];

for(int j = 0; j < shiftWidth; ++j)
string2[j] = '0';

}
else if(len2 > len1){
N = len2;

int shiftWidth = len2 - len1;

for( int i = len2 - 1; i >= 0; --i )
string1[i + shiftWidth] = string1[i];

for(int j = 0; j < shiftWidth; ++j)
string1[j] = '0';

}
else N = len1;

//printf("%s \n%s \n", string1, string2);

int k = N - 1;

// Multiply the numbers digit by digit and set in the lattice.
for( int i = 0; string2[i]; ++i ){
for( int j = 0; string2[j]; ++j ){

int num1 = string1[k] - '0';
int num2 = string2[j] - '0';

int multiply = num1 * num2;

node[j][k].upper = multiply / 10;
node[j][k].lower = multiply % 10;

}
--k;
}

//printMultiplicationMatrix();

// Lattice is divided into two parts upper left half and
// lower right half.

// result of upper half
int upperHalfResult[N];

// Add upper half
int i = N - 1;
for(; i >= 0; --i){
sum = 0;
m = 1;
upperHalfResult[i] = recursiveAdder(0, i);
}

// result of upper half
int lowerHalfResult[N];

// Add upper half
i = 0;
for(; i < N; ++i){
sum = 0;
m = 0;
lowerHalfResult[i] = recursiveAdder(i, N - 1);
}

// Combine upper and lower left half to a single array to fix addition
// problems.
int combinedRawResult[N + N];
i = 0;
for(; i < N; ++i )
combinedRawResult[i] = upperHalfResult[i];
for(k = 0; i < N + N; ++i, ++k )
combinedRawResult[i] = lowerHalfResult[k];

// If a cell has more than 9 then it should be added to the next cell.
for( int i = N + N - 1; i >= 0; --i ){

if( combinedRawResult[i] > 9 ){
combinedRawResult[i - 1] = combinedRawResult[i - 1] + combinedRawResult[i] / 10;
combinedRawResult[i] = combinedRawResult[i] % 10;
}

}

for(i = 0; i < N + N; ++i)
if(combinedRawResult[i]) break;

// print if the result can be printed or its zero.
bool zero = true;
for(; i < N + N; ++i){
printf("%d", combinedRawResult[i]);
zero = false;
}

// If the result is zero.
if( zero )
printf("0");

printf("\n");

}

return 0;
}


## UVA Problem 11988 – Broken Keyboard (a.k.a. Beiju Text) Solution

UVA Problem 11988 – Broken Keyboard (a.k.a. Beiju Text) Solution:

Click here to go to this problem in uva Online Judge.

Solving Technique:

The input may be classified into three things. One is append to beginning represented with ‘[‘, another is append to end represented with ‘]’ and the other types any other character except above mentioned. The other character are appended to the next position of last inserted character.

So task is move all characters following ‘[‘ to beginning until ‘]’ is found or end of string is reached. Similar logic applies to ‘]’ character. Also it is a recursive definition, keep applying this logic for all the following third brackets.

###### Other ideas:

Some other ideas to solve this problem can be, formatting the input to remove useless brackets then create a tree from inputs and perform in-order traversal to get the result. Another idea is create a linked list of strings.

###### Code Explanation:

I may later ( takes quite bit of time to create graphics ) provide a graphical representation of inserting in the doubly linked list ( 2nd code ). Meanwhile I provided a commented version ( 2nd code ) to make it a little easier to understand.

Here I have provided two codes. Both are linked list implementations. First one is singly linked list with no tail pointer( rather inefficient although I try to reduce some complexity by Boolean flag checking to reduce traversing the list to find tail pointer ). It is not able to keep track of tail pointer efficiently. Need to do some traversing ( some times almost the whole linked list ) to find the tail pointer.

The second implementation is doubly linked list with tail node as the tail pointer. The tail pointer has character has 0 which is ASCII decimal code for NULL character. I use this to stop printing otherwise a space character is printed at the end of output.

Important:  Be sure to add or print a new line after each output unless otherwise specified. The outputs should match exactly because sometimes even a space character causes the answer to be marked as wrong answer. Please compile with c++ compiler as some of my codes are in c and some in c++.

More Inputs of This Problem on uDebug.

Input:

This_is_a_[Beiju]_text
[[]][][]Happy_Birthday_to_Tsinghua_University


Output:

BeijuThis_is_a__text
Happy_Birthday_to_Tsinghua_University


### Code Singly Linked list Without Tail:

/**
* Author:    Asif Ahmed
* Site:      https://quickgrid.wordpress.com
* Problem:   UVA 11988 - broken keyboard
* Technique: Singly Linked List with no
*            tail Pointer(slow).
*/

#include<stdio.h>
#include<string.h>

#define N 100000

static char input[N];

struct vertex{
char c;
struct vertex* next;
};

typedef struct vertex node;

node* insertNode(node* n, char c){

node* temp = new node();
temp->c = c;
temp->next = n->next;
n->next = temp;

return temp;
}

void printList( node* dummy ){

node* tmp = dummy;

while( tmp = tmp->next )
putchar( tmp->c );

printf("\n");
}

int main(){

//freopen("input.txt", "r", stdin);
//freopen("output.txt", "w", stdout);

while( gets(input) ){

node* dummy = new node();
dummy->next = NULL;
node* cur = dummy;

node* tail = dummy;

bool rightopen = false;

for(int i = 0; input[i]; ++i){

if( input[i] == '[' ){
cur = dummy;
rightopen = true;
continue;
}
if( input[i] == ']' ){
rightopen = false;

node *tmp = tail;

while( tmp->next != NULL )
tmp = tmp->next;

tail = cur = tmp;
continue;
}

cur = insertNode(cur, input[i] );
if( !rightopen )
tail = cur;
}

printList( dummy );

}

return 0;
}


### Code Doubly Linked list With Tail Pointer:

/**
* Author:    Asif Ahmed
* Site:      https://quickgrid.wordpress.com
* Problem:   UVA 11988 - broken keyboard
* Technique: Doubly Linked List with
*            dummy tail node as Pointer.
*/

#include<stdio.h>
#include<string.h>

#define N 100000

static char input[N];

// Doubly linked list.
struct vertex{
char c;
struct vertex* next;
struct vertex* prev;
};
typedef struct vertex node;

node* insertNode(node* n, char c){

// Create the new node to hold current character.
node* temp = new node();
temp->c = c;

// Create forward connection from this created node
// to the next node of passed in node (n).
// Also create backward connection from the passed
// in node to current node.
temp->next = n->next;
n->next->prev = temp;

// Create forward connection from passed in node (n) to the
// newly created node (temp).
// Also create backward connection from created node to the
// passed in node.
n->next = temp;
temp->prev = n;

// return the pointer to the current node.
return temp;
}

void printList( node* dummy ){

// Dummy (head) is not a part of output.
node* tmp = dummy->next;

// Since I use tail pointer, check if its tail.
while( tmp->c ){
putchar( tmp->c );
tmp = tmp->next;
}

printf("\n");
}

int main(){

//freopen("input.txt", "r", stdin);
//freopen("output.txt", "w", stdout);

while( gets(input) ){

// Dummy node is just to keep track of beginning.
// It does not contain any input character.
// Tail is used to insert before the last node.
// Tail is also another dummy node keeps track of
// the end.
node* dummy = new node();
node* tail = new node();

// NULL may not be necessary since I use tail character
// checking to stop printing.
tail->prev = dummy;
dummy->next = tail;
tail->next = NULL;
dummy->prev = NULL;

// Set current node to dummy (beginning). Set tail
// to NULL character equivalent ASCII value.
node* cur = dummy;
tail->c = 0;

for(int i = 0; input[i]; ++i){

// Update node pointer to beginning based on bracket.
// If not bracket use previous pointer location.
if( input[i] == '[' ){
cur = dummy;
continue;
}
if( input[i] == ']' ){
cur = tail->prev;
continue;
}

cur = insertNode(cur, input[i] );
}

// Print output characters one by one.
printList( dummy );

}

return 0;
}


## Multi Digit Subtraction without Negative Checking in 8086 Assembly Language

##### Explanation:

This code preforms subtraction between two double digit numbers and prints their result. Note this works only if the digits of first number is bigger than second number. It doesn’t handle the exception that result can be negative.

##### Code:
;
; Author:  Asif Ahmed
; Site:    https://quickgrid.wordpress.com
; Comment: Semicolon means comment.
;

org 100h

.model small

.stack 200h

.data

msg1 db 'Enter first number: ', '$' msg2 db 'Enter first number: ', '$'
msg3 db 'The output is: ', '$' crlf db 0dh, 0ah, '$'

num1digit1 db ?
num1digit2 db ?
num2digit1 db ?
num2digit2 db ?

.code
.startup

; Show prompt for inputting first number

mov ah, 9
lea dx, msg1
int 21h

; Take input of the first digit for the first number

mov ah, 1
int 21h
mov num1digit1, al
sub num1digit1, 30h

; Take input of the second digit for the first number

mov ah, 1
int 21h
mov num1digit2, al
sub num1digit2, 30h

; Move cursor to a new line

mov ah, 9
lea dx, crlf
int 21h

; Prompt for input of second number

mov ah, 9
lea dx, msg2
int 21h

; Take input of the first digit for the second number

mov ah, 1
int 21h
mov num2digit1, al
sub num2digit1, 30h

; Take input of the second digit for the second number

mov ah, 1
int 21h
mov num2digit2, al
sub num2digit2, 30h

; Move cursor to new line

mov ah, 9
lea dx, crlf
int 21h

; show output message

mov ah, 9
lea dx, msg3
int 21h

;Print the first result digit

mov ah, 2
mov cl, num1digit1
sub cl, num2digit1
mov dl, cl
int 21h

;Print the second result digit

mov ah, 2
mov cl, num1digit2
sub cl, num2digit2
mov dl, cl
int 21h

.exit



## Simple Polynomial data structure and Calculator for single variable

##### Explanation:

The first code takes an integer for the value of the variable and the next one takes a double for the value of variable and produces value of the function.

I have commented the second code to make it easy. Pun intended on lines 144 to 147.

Calculates an equation with given value of the variable. If the equation is,

$f(x) = -50x^{-3} +3x -40x^2 +10x^{-5} -7x^{10}$

###### then for,

$x = -3, \ f(x) = -413710.189300 \\ x = -2, \ f(x) = -7328.062500 \\ x = -1, \ f(x) = -10.000000 \\ x = 0, \ \ \ f(x) = \ \ \ Undefined \\ x = 1, \ \ \ f(x) = -84.000000 \\ x = 2, \ \ \ f(x) = -7327.937500 \\ x = 3, \ \ \ f(x) = -413695.810700 \\$

(Pease Test this code before using, I haven’t done much testing). Check against this site. To use this from console comment freopen lines. Otherwise make two txt files named input and output in the same directory as the cpp file and follow the given equation input format.

##### Input:
-50x^-3 +3x^+1 -40x^+2 +10x^-5 -7x^+10
0
y
-3
y
-2
y
-1
y
0
y
1
y
2
y
3
n

##### Output:
-50x^-3 +3x^+1 -40x^+2 +10x^-5 -7x^+10
Calculate value of Equation for given value (y/n)?
Enter value for the variable.
>>	 -413710.189300
Calculate value of Equation for given value (y/n)?
Enter value for the variable.
>>	 -7328.062500
Calculate value of Equation for given value (y/n)?
Enter value for the variable.
>>	 -10.000000
Calculate value of Equation for given value (y/n)?
Enter value for the variable.
Sorry Try something different
Calculate value of Equation for given value (y/n)?
Enter value for the variable.
>>	 -84.000000
Calculate value of Equation for given value (y/n)?
Enter value for the variable.
>>	 -7327.937500
Calculate value of Equation for given value (y/n)?
Enter value for the variable.
>>	 -413695.810700
Calculate value of Equation for given value (y/n)?
Exiting...


#### Code:

/**
* Author:    Asif Ahmed
* Site:      https://quickgrid.wordpress.com
* Problem:   Simple Polynomial data structure and
*            Calculator for single variable.
*/

#include<stdio.h>
#include<string.h>
#include<math.h>

#define N 512

char input[N];

struct PolynomialEquation{

char sign;
char signExponent;
int exponent;
char variable;
int constant;

struct PolynomialEquation *next;
};
typedef struct PolynomialEquation node;

node* insertNode(node* current, char sign, int constant, char variable, char signExponent, int exponent){

node* temp = new node();

temp->sign = sign;
temp->signExponent = signExponent;
temp->exponent = exponent;
temp->variable = variable;
temp->constant = constant;

temp->next = NULL;
current->next = temp;
current = temp;

return current;
}

void printEquation(node* dummy){
node* tmp = dummy->next;
while( tmp != NULL ){
printf("%c%d%c^%c%d ", tmp->sign, tmp->constant, tmp->variable, tmp->signExponent, tmp->exponent);
tmp = tmp->next;
}
printf("\n");
}

void calculateEquation(node* dummy, int var){

double sum = 0;
bool calculable;

node* tmp = dummy->next;
while( tmp != NULL ){

double constantValue = 0, variableValue = 0;
calculable = true;

constantValue = tmp->constant;
if(tmp->sign == '-')
constantValue *= -1;

variableValue = pow(var, tmp->exponent);
if(tmp->signExponent == '-'){
if(variableValue)
variableValue = (double) 1 / variableValue;
else
calculable = false;
}

sum = sum + variableValue * constantValue;
tmp = tmp->next;

if(!calculable){
printf("Sorry Try something different\n");
break;
}

}

if(calculable)
printf(">>\t %f\n", sum);

}

int main(){

// Comment these lines to do I/O operation in console.
freopen("input.txt", "r", stdin);
freopen("output.txt", "w", stdout);

char sign;
char signExponent;
int exponent;
char variable;
int constant;

node* dummy = new node();
dummy->variable = '$'; node* current = dummy; while( scanf("%c%d%c%*c%c%d", &sign, &constant, &variable, &signExponent, &exponent ) == 5){ getchar(); current = insertNode(current, sign, constant, variable, signExponent, exponent); } printEquation(dummy); while(1){ printf("Calculate value of Equation for given value (y/n)?\n"); char choice = getchar(); if( choice == 'y' ){ printf("Enter value for the variable.\n"); int variableValue; scanf("%d", &variableValue); getchar(); calculateEquation(dummy, variableValue); }else{ printf("Exiting...\n"); break; } } return 0; }  ### Working with float numbers: If the equation is, $f(x) = - 4x^{2} - 4x - 9$ ##### Input: +4x^+2 -4x^+1 -9x^+0 0 y 5 y 2.5 y 1.25 y 1.875 n  ##### Output: +4x^+2 -4x^+1 -9x^+0 Calculate value of Equation for given value (y/n)? Enter value for the variable: >> 71.000000 Calculate value of Equation for given value (y/n)? Enter value for the variable: >> 6.000000 Calculate value of Equation for given value (y/n)? Enter value for the variable: >> -7.750000 Calculate value of Equation for given value (y/n)? Enter value for the variable: >> -2.437500 Calculate value of Equation for given value (y/n)? Exiting...  #### Code for float: /** * Author: Asif Ahmed * Site: https://quickgrid.wordpress.com * Problem: Simple Polynomial data structure and * Calculator with single variable. */ #include<stdio.h> #include<string.h> #include<math.h> #define N 512 char input[N]; struct PolynomialEquation{ char sign; char signExponent; int exponent; char variable; int constant; struct PolynomialEquation *next; }; typedef struct PolynomialEquation node; node* insertNode(node* current, char sign, int constant, char variable, char signExponent, int exponent){ node* temp = new node(); temp->sign = sign; temp->signExponent = signExponent; temp->exponent = exponent; temp->variable = variable; temp->constant = constant; temp->next = NULL; current->next = temp; current = temp; return current; } void printEquation(node* dummy){ // dummy is just an empty node to keep track of front of equation. // It is not part of equation. Equation starts after dummy node. node* tmp = dummy->next; // Print the equation term by term. while( tmp != NULL ){ printf("%c%d%c^%c%d ", tmp->sign, tmp->constant, tmp->variable, tmp->signExponent, tmp->exponent); tmp = tmp->next; } printf("\n"); } void calculateEquation(node* dummy, double var){ double sum = 0; bool calculable; // dummy->next because dummy node is not a part of the equation. node* tmp = dummy->next; while( tmp != NULL ){ double constantValue = 0, variableValue = 0; calculable = true; // make constant negative if the sign is negative. constantValue = tmp->constant; if(tmp->sign == '-') constantValue *= -1; // calculate the value of the variable with given exponent. variableValue = pow(var, tmp->exponent); if(tmp->signExponent == '-'){ if(variableValue) variableValue = (double) 1 / variableValue; else calculable = false; } // multiply the calculated value of variable with the constant. sum = sum + variableValue * constantValue; // calculate the next term of the equation. tmp = tmp->next; // If not calculable. Ex: divide by zero. then print this. if(!calculable){ printf("Sorry Try something different\n"); break; } } // print the result. if(calculable) printf(">>\t %f\n", sum); } int main(){ // Comment these lines to do I/O operation in console. //freopen("input.txt", "r", stdin); //freopen("output.txt", "w", stdout); char sign; char signExponent; int exponent; char variable; int constant; // Dummy node to make insertion code simpler. node* dummy = new node(); dummy->variable = '$';
node* current = dummy;

// Take input of equation term by term.
// If
//     taking input from console stop input using null terminator ( ctrl + z ).
// Else
//     when taking input from file enter a 0 in a line by itself to stop input.
while( scanf("%c%d%c%*c%c%d", &sign, &constant, &variable, &signExponent, &exponent ) == 5){
getchar();
current = insertNode(current, sign, constant, variable, signExponent, exponent);
}

// print the
printEquation(dummy);

// Enter different values for the variable to get the value of function.
while(1){
printf("Calculate value of Equation for given value (y/n)?\n");

char choice = getchar();

if( choice == 'y' ){
printf("Enter value for the variable:\n");

double variableValue;
scanf("%lf", &variableValue);
getchar();

calculateEquation(dummy, variableValue);
}else{
printf("Exiting...\n");
break;
}
}

return 0;
}