POJ 3669

#include<cstdio>
#include<cstring>
#include<queue>
using namespace std;
int dx[4]={+1,0,-1,0};
int dy[4]={0,+1,0,-1};
struct type{
    int x,y,t;
}meteor[50000+5],now,next;
int n,map[305][305],latest;
bool vis[305][305];
int bfs()
{
    memset(vis,0,sizeof(vis)); //初始化标记数组 
    queue<type> q;
    now.x=0;
    now.y=0;
    now.t=0;
    vis[now.x][now.y]=1;
    q.push(now);
    while(!q.empty())
    {
        now=q.front();q.pop();
        if(map[now.x][now.y] == 2139062143) return now.t; //如果当前这个格子的被流星摧毁时间是正无穷，那么已经安全
        for(int i=0;i<4;i++)
        {
            next.x=now.x+dx[i] , next.y=now.y+dy[i] , next.t=now.t+1 ;
            if(next.x >= 0 && next.y >= 0 && map[next.x][next.y] > next.t && !vis[next.x][next.y])
            {
                vis[next.x][next.y]=1;
                q.push(next);
            }
        }
    }
    return -1;
}
int main()
{
    while(scanf("%d",&n) != EOF)
    {
        memset(map,0x7F,sizeof(map)); //先将地图上每个格子初始化为“正无穷” 
        latest=-1;
        for(int i=1;i<=n;i++)
        {
            scanf("%d %d %d",&meteor[i].x,&meteor[i].y,&meteor[i].t);
            
            if(map[meteor[i].x][meteor[i].y] > meteor[i].t) map[meteor[i].x][meteor[i].y] = meteor[i].t; 
            for(int j=0;j<4;j++){
                next.x=meteor[i].x+dx[j];
                next.y=meteor[i].y+dy[j];
                if(map[ (next.x) ][ (next.y) ] > meteor[i].t) map[ (next.x) ][ (next.y) ] = meteor[i].t;
            } //将地图上的每个格子更新，使其值成为该格最早被流星摧毁的时间 
             
        }
        printf("%d
",bfs());
    }
}