BZOJ 1671: [Usaco2005 Dec]Knights of Ni 骑士 (bfs)

题目:

  https://www.lydsy.com/JudgeOnline/problem.php?id=1671

题解:
  按题意分别从贝茜和骑士bfs然后meet_in_middle。。

  把一个逗号打成分号调了20分钟。。。

代码:

 1 #include<bits/stdc++.h>
 2 
 3 using namespace std;
 4 
 5 const int mx[5]={0,-1,1,0,0},my[5]={0,0,0,-1,1};
 6 const int maxn=1010;
 7 int n,m,g[maxn][maxn],vis[maxn][maxn],f[maxn][maxn],sum,cnt,sx,sy,bx,by,flag,ans=0x3f3f3f3f;
 8 struct node{int x,y,num;};
 9 
10 int main(){
11     scanf("%d%d",&m,&n);
12     for(int i=1;i<=n;i++)
13         for(int j=1;j<=m;j++){
14             scanf("%d",&g[i][j]);
15             if(g[i][j]==2) sx=i,sy=j;
16             else if(g[i][j]==3) bx=i,by=j;
17             else if(g[i][j]==4) sum++;
18         }
19     queue<node> q; cnt=sum;
20     q.push((node){sx,sy,0}),vis[sx][sy]=1;
21     while(!q.empty()){
22         node now=q.front(); q.pop();
23         for(int i=1;i<=4;i++){
24             int xx=now.x+mx[i],yy=now.y+my[i];
25             if(xx>0&&xx<=n&&yy>0&&yy<=m&&!vis[xx][yy]&&g[xx][yy]!=1){
26                 if(g[xx][yy]==4&&f[xx][yy]==0) f[xx][yy]=now.num+1,cnt--;
27                 if(!cnt) goto end;
28                 q.push((node){xx,yy,now.num+1}); vis[xx][yy]=1;
29             }
30         }
31     }
32     end: memset(vis,0,sizeof(vis));
33     while(!q.empty()) q.pop(); cnt=sum;
34     q.push((node){bx,by,0}),vis[bx][by]=1;
35     while(!q.empty()){
36         node now=q.front(); q.pop();
37         for(int i=1;i<=4;i++){
38             int xx=now.x+mx[i],yy=now.y+my[i];
39             if(xx>0&&xx<=n&&yy>0&&yy<=m&&!vis[xx][yy]&&g[xx][yy]!=1){
40                 if(g[xx][yy]==4) ans=min(now.num+1+f[xx][yy],ans),cnt--;
41                 if(!cnt) goto print;
42                 q.push((node){xx,yy,now.num+1}); vis[xx][yy]=1;
43             }
44         }
45     }    
46     print:    printf("%d",ans);
47     return 0;    
48 }

 

posted @ 2018-04-19 08:30  Jack_the_Ripper  阅读(193)  评论(0编辑  收藏  举报