Flip Game

http://poj.org/problem?id=1753

#include<cstdio>
#include<algorithm>
#include<string.h>
using namespace std;

char s[6][6];
int a[6][6];
int deep,step,flag;
void inti(int row,int c)
{
    a[row-1][c]=!a[row-1][c];
    a[row][c+1]=!a[row][c+1];
    a[row+1][c]=!a[row+1][c];
    a[row][c-1]=!a[row][c-1];
    a[row][c]=!a[row][c];
}
int check()
{
    for(int i=1; i<=4; i++)
    {
        for(int j=1; j<=4; j++)
        {
            if(a[i][j]!=a[1][1]) return 0;
        }
    }
    return 1;
}
void dfs(int row,int c,int deep)
{
    if(deep==step)
    {
        flag=check();
        return;
    }
    if(flag||row==5) return;
    inti(row,c);
    if(c<4)
        dfs(row,c+1,deep+1);
    else
        dfs(row+1,1,deep+1);

    inti(row,c);
    if(c<4)
        dfs(row,c+1,deep);
    else
        dfs(row+1,1,deep);
    return ;
}
int main()
{
    memset(a,0,sizeof(a));
    for(int i=0; i<4; i++)
    {
        scanf("%s",s[i]);
    }
    for(int i=0; i<4; i++)
    {
        for(int j=0; j<4; j++)
        {
            if(s[i][j]=='b')
                a[i+1][j+1]=1;
        }
    }
    for(step=0; step<=16; step++)
    {
        dfs(1,1,0);
        if(flag)
        {
            printf("%d
",step);
            break;
        }
    }
    if(!flag) printf("Impossible
");
    return 0;
}