学步园

翻牌游戏，中间一个和上下左右全部反过来，知道全白或者全黑为止。

#include<iostream>
using namespace std;
int visited[65536];
int queue[65536];
int step[65536];
int front=0;
int rear=1;

int Flip(int s,int i)
{
	int mstate=s;

  	mstate^=1<<i;
	if ((i-4)>=0)
	{
		mstate ^=1<<(i-4);
	}
	if (i%4!=0)
	{
		mstate ^= 1<<(i-1);
	}
	if ((i+1)%4!=0)
	{
		mstate ^= 1<<(i+1);
	}
	if (i<12)
	{
		mstate ^= 1<<(i+4);
	}
	
	return mstate;
	
}
int BFS(int state)
{
	int depth=0;
	int s,i;
	queue[front]=state;
	visited[state]=1;
	if (state==0 || state==65535)
	{
		return 0;
	}
	while (front!=rear)
	{
			s=queue[front];
			front++;
			for (i=0;i<16;i++)
			{
				state=Flip(s,i);
				if (visited[state]==0)
				{
					queue[rear]=state;
					visited[state]=1;
					step[state]=step[s]+1;
					if (state==0 || state==65535)
					{
						return 1;
					}
					rear ++;
				}
			}
	}

		return -1;
}
int main(int argc,char *argv[])
{
	int state1=0;
	char str[17];
	int i=0;
	int k;
	memset(visited,0,sizeof(visited));
	memset(queue,0,sizeof(queue));
	memset(step,0,sizeof(step));
	while (i<16)
	{
		cin>>str[i];
		if (str[i]=='b')
		{
			state1 += 1<<i;
		}
		i++;
	}
	str[i]='\0';

	k=BFS(state1);
	switch (k)
	{
		case -1:
			cout<<"Impossible"<<endl;
			break;
		case 0:
			cout<<0<<endl;
			break;
		case 1:
			cout<<step[queue[rear-1]]<<endl;
			break;
	}
	return 0;
}