POJ1753【简单DFS算法】--翻棋盘（一步看不懂！！）

#include <stdio.h>

const int inf=9999999;
char s[10];
int map[10][10],i,j;
int ans=9999999;

int panduan()
{
    int x=map[0][0];
    for (i=0; i<4; i++)
    {
        for (j=0; j<4; j++)
        {
            if (map[i][j]!=x)
                return 0;
        }
    }
    return 1;
}

void fan (int x,int y)
{
    map[x][y]=!map[x][y];
    if (x - 1 >= 0)
        map[x-1][y]=!map[x-1][y];
    if (x + 1 < 4)
        map[x+1][y]=!map[x+1][y];
    if (y - 1 >= 0)
        map[x][y-1]=!map[x][y-1];
    if (y + 1 < 4)
        map[x][y+1]=!map[x][y+1];
}

int dfs (int x,int y,int t)
{
    int nx,ny;
    if ( panduan()==1)
    {
        if (ans > t)
            ans = t ;
        return 0;
    }
    if (x >= 4 || y >= 4)
        return 0;

    nx = (x + 1)%4;
    ny = y + ( x + 1 ) / 4;

    dfs (nx,ny,t);//两次dfs不知道啥意思。。。
    fan (x,y);

    dfs (nx,ny,t+1);
    fan (x,y);

    return 0;
}
int main ()
{
    for (i=0; i<4; i++)
    {
        scanf ("%s",s);
        for (j=0; j<4; j++)
        {
            if (s[j]==‘b‘)
                map[i][j]=0;
            else
                map[i][j]=1;
        }
    }
    dfs (0,0,0);

    if (ans == inf )
        printf ("Impossible\n");
    else printf ("%d\n",ans);
    return 0;
}