UVA 11624 Fire! BFS搜索

#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
[i]!=-1)
{
if(mp
[i]==-1||v
[i]<mp
[i])
ans=min(ans,v
[i]);
}
}
if(ans==INF)printf("IMPOSSIBLE\n");
else printf("%d\n",ans+1);
}
return 0;
}