Poj 3669 meteor shower

Http://poj.org/problem? Id = 3669

Question:

Given several coordinates, at the T moment, there will be a meteorite rain, and the upper and lower sides will also be damaged. How to find a safe place in the shortest time.

Train of Thought: pre-process the points around the whereabouts of each meteorite, and then BFS can.

 1 #include <cstdio> 2 #include <cstring> 3 #include <queue> 4 #include <algorithm> 5 #define maxn 50000 6 using namespace std; 7  8 int n; 9 int ans,max1;10 int vis[400][400];11 int dir[5][2]={{0,0},{0,1},{0,-1},{1,0},{-1,0}};12 struct node13 {14     int x,y;15     int t;16 }p[maxn],st1,st2;17 18 void bfs(int x,int y)19 {20     queue<node>q;21     st1.x=x;22     st1.y=y;23     st1.t=0;24     if(vis[x][y]==0)25     {26         return;27     }28     q.push(st1);29     while(!q.empty())30     {31         st2=q.front(); q.pop();32         if(vis[st2.x][st2.y]==-1)33         {34             ans=st2.t;35             return ;36         }37         for(int i=0; i<5; i++)38         {39             int x1=st2.x+dir[i][0];40             int y1=st2.y+dir[i][1];41             if(!(x1>=0&&y1>=0)) continue;42             if((vis[x1][y1]>st2.t+1)||(vis[x1][y1]==-1))43             {44                 if(vis[x1][y1]!=-1)45                 {46                     vis[x1][y1]=st2.t+1;47                 }48                 st1.x=x1;st1.y=y1;49                 st1.t=st2.t+1;50                 q.push(st1);51             }52         }53     }54 }55 56 int main()57 {58     while(scanf("%d",&n)!=EOF)59     {60         ans=-1;61         memset(vis,-1,sizeof(vis));62         for(int i=1; i<=n; i++)63         {64             scanf("%d%d%d",&p[i].x,&p[i].y,&p[i].t);65             for(int j=0; j<5; j++)66             {67                 int xx=p[i].x+dir[j][0];68                 int yy=p[i].y+dir[j][1];69                 if(!(xx>=0&&yy>=0)) continue;70                 if(vis[xx][yy]==-1)71                 {72                     vis[xx][yy]=p[i].t;73                 }74                 else75                 {76                     vis[xx][yy]=min(vis[xx][yy],p[i].t);77                 }78             }79         }80         bfs(0,0);81         printf("%d\n",ans);82     }83     return 0;84 }

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Poj 3669 meteor shower