UVA 11624 Fire! BFS搜索

题意：就是问你能不能在火烧到你之前，走出一个矩形区域，如果有，求出最短的时间

分析：两遍BFS，然后比较边界

#include<cstdio>
#include<algorithm>
#include<iostream>
#include<cstring>
#include<cmath>
#include<map>
#include<queue>
#include<stdlib.h>
#include<string>
#include<set>
using namespace std;
typedef long long LL;
const int maxn=;
const int INF=0x3f3f3f3f;
char s[maxn][maxn];
int mp[maxn][maxn];
int v[maxn][maxn];
int n,m;
struct Point
{
    int x,y;
    Point() {}
    Point(int a,int b)
    {
        x=a,y=b;
    }
} o,t;
queue<Point>q,e;
int dx[]= {,,-,};
int dy[]= {-,,,};
int main()
{
    int T;
    scanf("%d",&T);
    while(T--)
    {
        scanf("%d%d",&n,&m);
        for(int i=; i<=n; ++i)
            scanf("%s",s[i]+);
        for(int i=; i<=n; ++i)
        {
            for(int j=; j<=m; ++j)
            {
                mp[i][j]=v[i][j]=-;
                if(s[i][j]=='F')q.push(Point(i,j)),mp[i][j]=;
                else if(s[i][j]=='J')e.push(Point(i,j)),v[i][j]=;
            }
        }
        while(!q.empty())
        {
            o=q.front();
            q.pop();
            for(int i=; i<; ++i)
            {
                t.x=o.x+dx[i];
                t.y=o.y+dy[i];
                if(t.x<||t.x>n||t.y<||t.y>m)continue;
                if(s[t.x][t.y]=='#'||mp[t.x][t.y]!=-)continue;
                mp[t.x][t.y]=mp[o.x][o.y]+;
                q.push(t);
            }
        }
        while(!e.empty())
        {
            o=e.front();
            e.pop();
            for(int i=; i<; ++i)
            {
                t.x=o.x+dx[i];
                t.y=o.y+dy[i];
                if(t.x<||t.x>n||t.y<||t.y>m)continue;
                if(s[t.x][t.y]=='#'||v[t.x][t.y]!=-)continue;
                v[t.x][t.y]=v[o.x][o.y]+;
                e.push(t);
            }
        }
        int ans=INF;
        for(int i=;i<=n;++i)
        {
           if(v[i][]!=-)
           {
               if(mp[i][]==-||v[i][]<mp[i][])
                 ans=min(ans,v[i][]);
           }
           if(v[i][m]!=-)
           {
               if(mp[i][m]==-||v[i][m]<mp[i][m])
                 ans=min(ans,v[i][m]);
           }
        }
        for(int i=;i<=m;++i)
        {
           if(v[][i]!=-)
           {
               if(mp[][i]==-||v[][i]<mp[][i])
                ans=min(ans,v[][i]);
           }
           if(v[n][i]!=-)
           {
               if(mp[n][i]==-||v[n][i]<mp[n][i])
                ans=min(ans,v[n][i]);
           }
        }
        if(ans==INF)printf("IMPOSSIBLE\n");
        else printf("%d\n",ans+);
    }
    return ;
}