POJ-1324-bfs,位运算

题目大意：贪吃蛇游戏，要到出口所需要的最小步数；

题目解析：bfs的时候因为要考虑到身体的状态所以我们需要借助位运算，来判断下一个蛇的身体和上一个的关系；

AC代码：

#include<iostream>#include<cstdio>#include<cstring>#include<string>#include<algorithm>#include<queue>using namespace std;const int maxn=25;int n,m,len,l;bool rock[maxn][maxn],vis[maxn][maxn][1<<14];int dir[4][2]={{-1,0},{1,0},{0,-1},{0,1}};struct snake{int head_x,head_y;int shape,step;snake(int a,int b,int c,int d){head_x=a;head_y=b;step=c;shape=d;}snake(){head_y=head_x=shape=step=0;}};snake s;void input_snake(){int last_x,last_y;scanf("%d%d",&s.head_x,&s.head_y);last_x=s.head_x;last_y=s.head_y;s.shape=s.step=0;for(int i=0;i<l-1;i++){int x,y;scanf("%d%d",&x,&y);if(y==last_y){if(x==last_x-1)s.shape|=0<<(i<<1);elses.shape|=1<<(i<<1);}else {if(y==last_y-1)s.shape|=2<<(i<<1);else s.shape|=3<<(i<<1); }last_y=y;last_x=x;}}bool ok(int x,int y,snake now){int tx=now.head_x;int ty=now.head_y;for(int i=0;i<l-1;i++){int d=(now.shape>>(i<<1))&3;int dx=tx+dir[d][0];int dy=ty+dir[d][1];if(dx==x&&dy==y)return false;tx=dx;ty=dy;}return true;} bool can_move(int x,int y,snake now){if(x>=1&&x<=n&&y<=m&&y>=1&&ok(x,y,now)&&!rock[x][y])return true;return false;}int change_shape(snake now,int d){int ts=now.shape;ts=ts<<2;ts&=len;if(d==0)d=1;else if(d==1)d=0;else if(d==2)d=3;elsed=2;ts|=d;return ts; }int bfs(){memset(vis,0,sizeof(vis));queue<snake>q;q.push(s);vis[s.head_x][s.head_y][s.shape]=1;while(!q.empty()){snake now = q.front();q.pop();//cout<<now.head_x<<" "<<now.head_y<<endl;if(now.head_x==1&&now.head_y==1)return now.step;for(int i=0;i<4;i++){int tx=now.head_x+dir[i][0];int ty=now.head_y+dir[i][1];if(!can_move(tx,ty,now))continue;snake next;next.shape=change_shape(now,i);next.head_x=tx;next.head_y=ty;if(!vis[tx][ty][next.shape]){vis[tx][ty][next.shape]=1;next.step=now.step+1;q.push(next);}}}return -1;}int main(){int num_case=1;while(scanf("%d%d%d",&n,&m,&l)!=EOF&&(n+m+l)){memset(rock,0,sizeof(rock));len=(1<<( (l-1)<<1) )-1;input_snake();int k;scanf("%d",&k);for(int i=0;i<k;i++){int x,y;scanf("%d%d",&x,&y);rock[x][y]=1;} printf("Case %d: %d\n",num_case++, bfs());  }return 0;}