P2895 [USACO08FEB]流星雨Meteor Shower

給每個點標記一下能夠走的最遲時間，藍後bfs處理一下

 1 #include<iostream>
 2 #include<cstdio>
 3 #include<cstring>
 4 #include<algorithm>
 5 #include<cctype>
 6 #include<queue>
 7 #define re register
 8 using namespace std;
 9 void read(int &x){
 
10     char c=getchar();x=0;
11     while(!isdigit(c)) c=getchar();
12     while(isdigit(c)) x=(x<<3)+(x<<1)+(c^48),c=getchar();
13 }
14 int min(int a,int b){return a<b?a:b;}
15 #define N 310
16 const int d1[5]={1,0,-1,0,0};
17 const int d2[5]={0,1,0,-1,0};
18 struct node{int x,y,t;}a;
 
19 queue <node> h;
20 int m,tp=1,ans,dan[N][N],win; bool vis[N][N];
21 int main(){
22     memset(dan,127,sizeof(dan)); int inf=dan[0][0];
23     read(m);
24     for(re int i=1;i<=m;++i){
25         read(a.x);read(a.y);read(a.t);
26         ++a.x; ++a.y;
27         dan[a.x][a.y]=min(dan[a.x][a.y],a.t);
 
28         dan[a.x][a.y+1]=min(dan[a.x][a.y+1],a.t);
29         dan[a.x][a.y-1]=min(dan[a.x][a.y-1],a.t);
30         dan[a.x+1][a.y]=min(dan[a.x+1][a.y],a.t);
31         dan[a.x-1][a.y]=min(dan[a.x-1][a.y],a.t);
32     }//處理每個點能走的最遲時間
33     h.push((node){1,1,0}); vis[1][1]=1;
34     if(dan[1][1]==inf) win=1,ans=0;
35     while(!h.empty()&&!win){
36         node u=h.front(); h.pop();
37         for(re int i=0;i<5&&!win;++i){
38             int r1=u.x+d1[i],r2=u.y+d2[i];
39             if(r1<1||r2<1||r1>=N||r2>=N) continue;
40             if(vis[r1][r2]||dan[r1][r2]<=u.t+1) continue;
41             if(dan[r1][r2]==inf) win=1,ans=u.t+1;
42             else h.push((node){r1,r2,u.t+1}),vis[r1][r2]=1;
43         }
44     }win ? printf("%d",ans):printf("-1");
45     return 0;
46 }

bzoj1611 / P2895 [USACO08FEB]流星雨Meteor Shower