UVA 11624 Fire!(图论BFS)

https://cn.vjudge.net/problem/UVA-11624

先对火做一次bfs处理出经过的所有点的时间，再对人bfs，满足时间小于火的

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<queue>
#define maxn 1500
#define inf 0x3f3f3f3f
using namespace std;
int sx,sy;
struct node
{
    int x,y,time;
};
int r,c;
char mp[maxn][maxn];
int dx[4]={1,-1,0,0};
int dy[4]={0,0,1,-1};
int vis[maxn][maxn];
int f[maxn][maxn];
queue<node>qf;

void fbfs()
{
  node u,v;
    while(!qf.empty())
    {
        u=qf.front();
        qf.pop();
        for(int i=0;i<4;i++)
        {
            v.x=u.x+dx[i];
            v.y=u.y+dy[i];
            v.time=u.time+1;
            if(mp[v.x][v.y]!='#'&&!vis[v.x][v.y]&&v.x>=0&&v.x<r&&v.y>=0&&v.y<c)
            {

               qf.push(v);
               vis[v.x][v.y]=1;
               if(v.time<f[v.x][v.y])
                f[v.x][v.y]=v.time;
            }
        }
    }


}
int jbfs()
{queue<node>q;
    memset(vis,0,sizeof(vis));
    node u,v,w;
    vis[sx][sy]=1;
    u.x=sx;
    u.y=sy;
    u.time=0;
    q.push(u);
    while(!q.empty())
    {
        v=q.front();
        q.pop();
        for(int i=0;i<4;i++)
        {
            w.x=v.x+dx[i];
            w.y=v.y+dy[i];
            w.time=v.time+1;
            if(w.x>=0&&w.x<r&&w.y>=0&&w.y<c)
            {if(mp[w.x][w.y]!='#'&&!vis[w.x][w.y]&&w.time<f[w.x][w.y])

               {

               q.push(w);
                vis[w.x][w.y]=1;
               }
            }
            else
            {
                return w.time;
            }
        }
    }
    return -1;
}

int main()
{
    int t;

    scanf("%d", &t);
    while(t--)
    {
        scanf("%d%d", &r, &c);
        for(int i = 0; i < r; i++)
            scanf("%s", mp[i]);
        for(int i = 0; i < r; i++)
            for(int j = 0; j < c; j++)
                f[i][j] = inf;  //初始化时间
        while(!qf.empty())    //清空队列
            qf.pop();
        struct node temp;
        for(int i = 0; i < r; i++)
            for(int j = 0; j < c; j++)
            {
                if(mp[i][j] == 'F')
                {
                    temp.x = i;
                    temp.y = j;
                    temp.time = 0;
                    qf.push(temp);  //每一个着火点入队
                    vis[i][j] = 1;
                }
                else if(mp[i][j] == 'J')
                {
                    sx = i;
                    sy = j;
                }
            }
        memset(vis, 0, sizeof(vis));
        fbfs();
        int cnt = jbfs();
        if(cnt!=-1)
            printf("%d\n", cnt);
        else
            printf("IMPOSSIBLE\n");
    }
    return 0;
}