图论基础UVA11624

#include<stdio.h>
#include<string.h>
#include<stdlib.h>
const int maxn=1010;
struct node{
	int x,y,s;
};
char str[maxn];
bool p[maxn][maxn],a[maxn][maxn];
int t[maxn][maxn],d[4][2]={{1,0},{0,1},{-1,0},{0,-1}};
struct node q[maxn*maxn];
void din(int i,int x1,int y1,int s1){
	q[i].x=x1;q[i].y=y1;q[i].s=s1;
}
int main(){
#ifndef ONLINE_JUDGE
	freopen("uva11624.in","r",stdin);
	freopen("uva11624.out","w",stdout);
#endif
	int i,j,k,k1,m,n;
	int xs,ys,e,T;
	int f,l,u,v,w;
	scanf("%d",&T);
	while(T--){
		memset(p,0,sizeof(p));
		memset(a,0,sizeof(a));		
		scanf("%d%d",&n,&m);
		for(i=1;i<=n;i++)
			for(j=1;j<=m;j++)
				t[i][j]=999999;
		f=0;l=0;
		getchar();
		for(i=1;i<=n;i++){
			gets(str);
			for(j=0;j<m;j++){
				if(str[j]!='#')
					a[i][j+1]=1;
				if(str[j]=='J'){
					xs=i;ys=j+1;					
				}
				if(str[j]=='F'){					
					din(++l,i,j+1,0);
					p[i][j+1]=1;
					t[i][j+1]=0;
				}
			}		
		}
		if(xs==1 || xs==n || ys==1 || ys==m){
			printf("1\n");
			continue;
		}
		
		while(f<l){
			f++;
			u=q[f].x;v=q[f].y;w=q[f].s;
			for(i=0;i<=3;i++)
				if(!p[u+d[i][0]][v+d[i][1]] && a[u+d[i][0]][v+d[i][1]]){
					p[u+d[i][0]][v+d[i][1]]=1;
					din(++l,u+d[i][0],v+d[i][1],w+1);
					t[u+d[i][0]][v+d[i][1]]=w+1;
				}			
		}
		memset(p,0,sizeof(p));
		int flag=0,ans;
		f=0;l=1;
		din(1,xs,ys,0);
		while(f<l){
			++f;
			u=q[f].x;v=q[f].y;w=q[f].s;
			for(i=0;i<=3;i++)
				if(!p[u+d[i][0]][v+d[i][1]] && a[u+d[i][0]][v+d[i][1]] && (w+1)<t[u+d[i][0]][v+d[i][1]]){
					p[u+d[i][0]][v+d[i][1]]=1;
					din(++l,u+d[i][0],v+d[i][1],w+1);					
					if(q[l].x==1 || q[l].x==n || q[l].y==1 || q[l].y==m){
						ans=q[l].s+1;flag=1;break;
					}
				}
			if(flag)break;
		}
		if(flag)
			printf("%d\n",ans);
		else puts("IMPOSSIBLE");
	}
	return 0;
}