Fire!---BFS

Fire! - UVA 11624 - Virtual Judge https://cn.vjudge.net/problem/UVA-11624


稍微有一点麻烦的BFS，要进行两次BFS，一次处理火焰到达各点的时间，另一次判断人到达各点的时间是否会超过火焰，如果超过就不能走过去，所以两次BFS中必须先进行处理火焰的BFS，不会着火的话就将时间设置为无穷大，永远无法到达，火焰可以上下左右四个方向扩散；
PS：火源可能不止一个
花了点时间补完了几道搜索题，爽歪歪

#include<bits/stdc++.h>
using namespace std;
const int Maxn=1005;
const int inf = 0x3f3f3f3f;
int visf[Maxn][Maxn],vism[Maxn][Maxn]; 
int dix[4]={-1,1,0,0};
int diy[4]={0,0,1,-1};
int jx,jy,fx,fy,t,n,m;
int firetime[1005][1005];
int mantime[1005][1005];
char maze[Maxn][Maxn];
int ans;
struct node{
	int x,y,step;
};
node Now,Next; 
queue<node>q;
void bfs_fire(){
	ios::sync_with_stdio(false);
    cin.tie(0);
	while(!q.empty()){
		Now=q.front();q.pop();
		for(int i=0;i<4;i++){
			int x=Now.x+dix[i];
			int y=Now.y+diy[i];
			if(x>=1&&x<=n&&y>=1&&y<=m&&maze[x][y]!='#'){
				Next=Now;
				if(!visf[x][y]){
					visf[x][y]=1;
					Next.x=x;
					Next.y=y;
					Next.step=Now.step+1;
					firetime[x][y]=Next.step;//记录火焰到达的时间 
					q.push(Next);
					
				}
			}
		}
	}
	
	
}
bool  bfs_man(){
	while(!q.empty())q.pop();
	Now.x=jx;Now.y=jy;Now.step=0;q.push(Now);
	vism[jx][jy]=1;
	while(!q.empty()){
		Now=q.front();q.pop();
		if(Now.x==1||Now.x==n||Now.y==1||Now.y==m){//走出迷宫 
			ans=Now.step+1;
			return true;
		} 
		
		for(int i=0;i<4;i++){
			int x=Now.x+dix[i];
			int y=Now.y+diy[i];
			if(Now.step+1>=firetime[x][y])continue;//到达该点时间比火焰长 
			if(x>=1&&x<=n&&y>=1&&y<=m&&maze[x][y]!='#'){
				Next=Now;
				if(!vism[x][y]){
					vism[x][y]=1;
					Next.x=x;
					Next.y=y;
					Next.step=Now.step+1;
					q.push(Next);
					
				}
			}
		}
	}
	return false;
	
}
int main()
{	
	cin>>t;
	while(t--){
		memset(visf,0,sizeof(visf));
		memset(vism,0,sizeof(vism));
		memset(firetime,inf,sizeof(firetime));
		//memset(mantime,0,sizeof(mantime));
		while(!q.empty())q.pop();
		cin>>n>>m;
		
		for(int i=1;i<=n;i++){
			for(int j=1;j<=m;j++){
				cin>>maze[i][j];
				
				
			}
		}
		
		//检索位置 
		for(int i=1;i<=n;i++){
			for(int j=1;j<=m;j++){
				if(maze[i][j]=='J'){
					jx=i;
					jy=j;
				}
				if(maze[i][j]=='F'){//火源不止一个 
					Now.x=i;Now.y=j;Now.step=0;
					firetime[i][j]=0;
					visf[i][j]=1;
					q.push(Now);
					
					//maze[i][j]='#';
				}
			}
		}
		
		bfs_fire();//处理火焰时间 
		
		if(bfs_man())cout<<ans<<endl;
		else cout<<"IMPOSSIBLE"<<endl;
		ans=0;
		//int ans=bfs2(); 
		
	} 
	
	return 0;
}