学步园

裸爆搜。但是要注意搜索方法..

可参考http://blog.csdn.net/lyy289065406/article/details/6642595

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

using namespace std;

int a[10][10];
char c[10][10];
int tt;
bool flag;

void flip(int x, int y)
{
	a[x][y] = 1 - a[x][y];
	a[x+1][y] = 1 - a[x+1][y];
	a[x-1][y] = 1 - a[x-1][y];
	a[x][y-1] = 1 - a[x][y-1];
	a[x][y+1] = 1 - a[x][y+1];
}

int OK()
{
	int x = 0;
	for( int i = 1; i <= 4; i ++ )
		for( int j = 1; j <= 4; j ++ )
			x += a[i][j];
	if( x == 0 || x == 16 )
		return 1;
	else
		return 0;
}

void dfs(int x, int y, int t)
{
	if( t == tt )
	{
		flag = OK();
		return;
	}
	if( flag || x == 5 )
		return;
	flip(x, y);
	if( y < 4 )
		dfs(x, y+1, t+1);
	else
		dfs(x+1, 1, t+1);
	flip(x, y);
	if( y < 4 )
		dfs(x, y+1, t);
	else
		dfs(x+1, 1, t);
	return;
}

int main()
{
	while(~scanf("%s", c[1]+1))
	{
		for( int i = 2; i <= 4; i ++ )
		{
			scanf("%s", c[i] + 1);
		}
		for( int i = 1; i <= 4; i ++ )
		{
			for( int j = 1; j <= 4; j ++ )
				a[i][j] = (c[i][j] == 'w' ? 0: 1);
		}
		flag = 0;
		for( tt = 0; tt <= 16; tt ++ )
		{
			dfs(1, 1, 0);
			if( flag )
				break;
		}
		if( flag )
			printf("%d\n", tt);
		else
			printf("Impossible\n");
	}
	return 0;
}

/*

bwwb
bbwb
bwwb
bwww

*/