Tuesday, January 10, 2012

Maximum size Square Sub matrix with all 1s

For example, consider the below binary matrix.
0  1  1  0  1
   1  1  0  1  0
   0  1  1  1  0
   1  1  1  1  0
   1  1  1  1  1
   0  0  0  0  0
The maximum square sub-matrix with all set bits is
1  1  1
    1  1  1
    1  1  1
http://www.geeksforgeeks.org/maximum-size-sub-matrix-with-all-1s-in-a-binary-matrix/
 
Method 1:Dynamic Programming
#include<stdio.h>
#define bool int
#define R 6
#define C 5

int min(int a, int b, int c)
{
  int m = a;
  if (m > b)
    m = b;
  if (m > c)
    m = c;
  return m;
}
  
void printMaxSubSquare(bool M[R][C])
{
  int i,j;
  int S[R][C];
  int max_of_s, max_i, max_j;
 
  for(i = 0; i < R; i++)
     S[i][0] = M[i][0];
 
  for(j = 0; j < C; j++)
     S[0][j] = M[0][j];
 
  for(i = 1; i < R; i++)
  {
    for(j = 1; j < C; j++)
    {
      if(M[i][j] == 1)
        S[i][j] = min(S[i][j-1], S[i-1][j], S[i-1][j-1]) + 1;
      else
        S[i][j] = 0;
    }
  }

  max_of_s = S[0][0]; max_i = 0; max_j = 0;
  for(i = 0; i < R; i++)
  {
    for(j = 0; j < C; j++)
    {
      if(max_of_s < S[i][j])
      {
         max_of_s = S[i][j];
         max_i = i;
         max_j = j;
      }
    }
  }    
 
  printf("\nMaximum size sub-matrix is: \n");
  for(i = max_i; i > max_i - max_of_s; i--)
  {
    for(j = max_j; j > max_j - max_of_s; j--)
    {
      printf("%d ", M[i][j]);
    }
    printf("\n");
  }
}    
 
int main()
{
  bool M[R][C] =  {{0, 1, 1, 0, 1},
                   {1, 1, 0, 1, 0},
                   {0, 1, 1, 1, 0},
                   {1, 1, 1, 1, 0},
                   {1, 1, 1, 1, 1},
                   {0, 0, 0, 0, 0}};
 
  printMaxSubSquare(M);
  getchar();
}
Time Complexity:  O(m*n) where m is number of rows and n is number of columns in 
the given matrix.
Auxiliary Space: O(m*n) where m is number of rows and n is number of columns in 
the given matrix.

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