UVA 11624 Fire!

数据：

3
4 4
####
#JF#
#..#
#..#
3 3
FFF
FJF
FFF
3 3
...
.J.
...

嗯，被第三个数据卡啦半天....

两次BFS  预处理一下每个点最早着火的时间.

/* ***********************************************
Author        :pk29
Created Time  :2015/8/19 19:26:13
File Name     :4.cpp
************************************************ */
#include <iostream>
#include <cstring>
#include <cstdlib>
#include <stdio.h>
#include <algorithm>
#include <vector>
#include <queue>
#include <set>
#include <map>
#include <string>
#include <math.h>
#include <stdlib.h>
#include <iomanip>
#include <list>
#include <deque>
#include <stack>
#define ull unsigned long long
#define ll long long
#define mod 90001
#define INF 0x3f3f3f3f
#define maxn 10000+10
#define cle(a) memset(a,0,sizeof(a))
const ull inf = 1LL << 61;
const double eps=1e-5;
using namespace std;
struct node{
    int x,y,dist;
};
bool cmp(int a,int b){
    return a>b;
}
int dir[4][2]={1,0,0,1,0,-1,-1,0};
char mp[1100][1100];
int vis[1100][1100],val[1100][1100];
int n,m,sx,sy,fx,fy;
queue<node>p;
void bfs1(){
    cle(vis);
    node u,v;
    while(!p.empty()){
        u=p.front(),p.pop();
        for(int i=0;i<4;i++){
            int nx=u.x+dir[i][0];
            int ny=u.y+dir[i][1];
            if(!vis[nx][ny]&&nx<=n&&ny>=1&&nx>=1&&ny<=m&&mp[nx][ny]=='.'){
                v.x=nx,v.y=ny,v.dist=u.dist+1;
                vis[nx][ny]=1;
                val[nx][ny]=v.dist;
                p.push(v);
            }
        }
    }
}
queue<node>q;
void bfs2(){
    int mark=0;
    cle(vis);
    while(!q.empty())q.pop();
    node u,v;
    u.x=sx,u.y=sy,u.dist=0;
    q.push(u);
    vis[u.x][u.y]=1;
    while(!q.empty()){
        u=q.front(),q.pop();
        if(u.x==n||u.x==1||u.y==1||u.y==m){
            mark=1;printf("%d
",u.dist+1);break;
        }
        for(int i=0;i<4;i++){
            int nx=u.x+dir[i][0];
            int ny=u.y+dir[i][1];
            if(vis[nx][ny]==0&&nx<=n&&ny>=1&&nx>=1&&ny<=m&&mp[nx][ny]=='.'){
                v.dist=u.dist+1;
                if(v.dist<val[nx][ny]){
                    v.x=nx,v.y=ny;
                    q.push(v);
                    vis[nx][ny]=1;
                }
            }
        }
    }
    if(!mark)printf("IMPOSSIBLE
");
}
int main()
{
    #ifndef ONLINE_JUDGE
    freopen("in.txt","r",stdin);
    #endif
    //freopen("out.txt","w",stdout);
    int t;
    cin>>t;
    while(t--){
        cin>>n>>m;
        cle(mp);
        memset(val,INF,sizeof val);
        for(int i=1;i<=n;i++)
            for(int j=1;j<=m;j++){
                cin>>mp[i][j];
                if(mp[i][j]=='J'){
                    sx=i,sy=j;
                }
                if(mp[i][j]=='F'){
                    node o;o.x=i,o.y=j,o.dist=0;
                     p.push(o);
                }
            }
        bfs1();
        bfs2();
    }
    return 0;
}