Max Same Letter Square Size

             Max Same Letter Square Size 

Certain kids were playing a game in which they would draw a N*N matrix and would fill in a letter from A to Z in a given cell based on certain rules.
Without getting into the details of those rules, the final values present in the N*N matrix is passed as the input to the program.
The program must print the size of the largest square sub-matrix which has all the letters equal in it.

Input Format:
The first line will contain N.
The next N lines will each contain N letters separated by a space.

Output Format:
The first line will contain the size of the largest square sub-matrix with all the letters equal in it.

Boundary Conditions:
3 <= N <= 50

Example Input/Output 1:
 Input:
5
A H K L O
 J H H B U
Q H H H Z
 I E H H W
F H H W Z

 Output:
2
Explanation: 
The two 2*2 sub-matrices filled with H are the largest.

Example Input/Output 1: 
Input:
7
B C C C C J K
O P Q R S T C
 H S S S S S S
 J K S S S S S
 K I S S S S U
 G H S S S S V
 Y Y Y X D Q T


Output:
  4

Explanation:

The 4*4 sub-matrix filled with S is the largest.


Code:

#include <iostream>

using namespace std;

int main(){

 int num,i,j,c,x,y,k,l,max=0;

 cin>>num;

 char a[num][num];

 for(i=0;i<num;i++)

 for(j=0;j<num;j++)

 cin>>a[i][j];

 for(i=0;i<num;i++)

 {

 for(j=0;j<num;j++)

 {

     if(a[i][j]==a[i][j+1] && a[i][j]==a[i+1][j])

     {

         x=0;

         y=0;

         for(k=i;k<num;k++){

         if(a[k][j]!=a[i][j])

             break;

             x++;

         }

         for(k=j;k<num;k++){

         if(a[i][k]!=a[i][j])

         break;

         y++;

         }

         c= min(x,y);

     }   

     for(k=i;k<i+c;k++){

     for(l=j;l<j+c;l++)

     if(a[k][l]!=a[i][j])

     break;

         if(j+c>l)

         break;

         }

         if(k==i+c && l==j+c && max<c)

         max=c;

 }

 }

 cout<<max;

 return 0;

}