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=1005;
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[4]= {0,0,-1,1};
int dy[4]= {-1,1,0,0};
int main()
{
    int T;
    scanf("%d",&T);
    while(T--)
    {
        scanf("%d%d",&n,&m);
        for(int i=1; i<=n; ++i)
            scanf("%s",s[i]+1);
        for(int i=1; i<=n; ++i)
        {
            for(int j=1; j<=m; ++j)
            {
                mp[i][j]=v[i][j]=-1;
                if(s[i][j]=='F')q.push(Point(i,j)),mp[i][j]=0;
                else if(s[i][j]=='J')e.push(Point(i,j)),v[i][j]=0;
            }
        }
        while(!q.empty())
        {
            o=q.front();
            q.pop();
            for(int i=0; i<4; ++i)
            {
                t.x=o.x+dx[i];
                t.y=o.y+dy[i];
                if(t.x<1||t.x>n||t.y<1||t.y>m)continue;
                if(s[t.x][t.y]=='#'||mp[t.x][t.y]!=-1)continue;
                mp[t.x][t.y]=mp[o.x][o.y]+1;
                q.push(t);
            }
        }
        while(!e.empty())
        {
            o=e.front();
            e.pop();
            for(int i=0; i<4; ++i)
            {
                t.x=o.x+dx[i];
                t.y=o.y+dy[i];
                if(t.x<1||t.x>n||t.y<1||t.y>m)continue;
                if(s[t.x][t.y]=='#'||v[t.x][t.y]!=-1)continue;
                v[t.x][t.y]=v[o.x][o.y]+1;
                e.push(t);
            }
        }
        int ans=INF;
        for(int i=1;i<=n;++i)
        {
           if(v[i][1]!=-1)
           {
               if(mp[i][1]==-1||v[i][1]<mp[i][1])
                 ans=min(ans,v[i][1]);
           }
           if(v[i][m]!=-1)
           {
               if(mp[i][m]==-1||v[i][m]<mp[i][m])
                 ans=min(ans,v[i][m]);
           }
        }
        for(int i=1;i<=m;++i)
        {
           if(v[1][i]!=-1)
           {
               if(mp[1][i]==-1||v[1][i]<mp[1][i])
                ans=min(ans,v[1][i]);
           }
           if(v[n][i]!=-1)
           {
               if(mp[n][i]==-1||v[n][i]<mp[n][i])
                ans=min(ans,v[n][i]);
           }
        }
        if(ans==INF)printf("IMPOSSIBLE\n");
        else printf("%d\n",ans+1);
    }
    return 0;
}