POJ 1753 Flip Game 简单BFS

 1 #include <stdio.h>
 2 #include <string.h>
 3 int st;
 4 char s[10];
 5 int q[70000],vis[70000],front,tail;
 6 const int dx[]={1,-1,0,0};
 7 const int dy[]={0,0,1,-1};
 8 int BFS() {
 9     front=tail=0;
10     memset(vis,-1,sizeof(vis));
11     q[tail++]=st;
12     vis[st]=0;
13     while (front!=tail) {
14         int u=q[front++];
15         if (!u||u==65535)
16             return vis[u];
17         for (int x=0;x<4;x++)
18             for (int y=0;y<4;y++) {
19                 int v=u;
20                 v^=1<<((x<<2)+y);
21                 for (int j=0;j<4;j++) {
22                     int nx=x+dx[j],ny=y+dy[j];
23                     if (0<=nx&&nx<4&&0<=ny&&ny<4) {
24                         v^=1<<((nx<<2)+ny);
25                     }
26                 }
27                 if (vis[v]==-1) {
28                     vis[v]=vis[u]+1;
29                     q[tail++]=v;
30                 }
31             }
32     }
33     return -1;
34 }
35 
36 int main() {
37     while (~scanf("%s",s)) {
38         st=0;
39         for (int i=0;i<4;i++)
40             st=st<<1|(s[i]==‘b‘);
41         for (int j=0;j<3;j++) {
42             scanf("%s",s);
43             for (int i=0;i<4;i++)
44                 st=st<<1|(s[i]==‘b‘);
45         }
46         int ans=BFS();
47         if (ans==-1)
48             puts("Impossible");
49         else
50             printf("%d\n",ans);
51     }
52     return 0;
53 }