不判空居然没问题 判空AC：

#include <bits/stdc++.h>
#define LL long long
using namespace std;
const int N = 30 + 10;
const int INF = 0x3f3f3f3f;
struct node
{
	int x , y , z , time;
};
queue < node > q;
bool flag;
int dx [] = {1 , -1 , 0 , 0 , 0 , 0};
int dy [] = {0 , 0 , 1 , -1 , 0 , 0};
int dz [] = {0 , 0 , 0 , 0 , 1 , -1};
int l , n , m , sx , sy , sz , ex , ey , ez; 
char a [N] [N] [N];
bool check (int x , int y , int z)
{
	if (x >= 1 && x <= l && y >= 1 && y <= n && z >= 1 && z <= m && a [x][y][z] != '#')
	    return 1;
	return 0;
}
void bfs (int x , int y , int z)
{
	a [x] [y] [z] = '#';
	q.push((node) {x , y , z , 0});
	while ( !q.empty() )
	{
		node top = q.front();
		q.pop(); 
		if (top.x == ex && top.y == ey && top.z == ez)
		{
			printf ("%s%d%s\n" , "Escaped in " , top.time , " minute(s).");
			flag = 1;
			return;
		}
		for (int i = 0; i <= 5; i++)
		{
			int xx = top.x + dx [i]; 
			int yy = top.y + dy [i]; 
			int zz = top.z + dz [i];
			if (check (xx , yy , zz)) 
			{
				q.push((node) {xx , yy , zz , top.time + 1});
				a [xx] [yy] [zz] = '#';
			}
		}
	}
}
int main()
{
	    while (cin >> l >> n >> m)
	    {
	    	if (l == 0 && n == 0 && m == 0) return 0;
	    	for (int i = 1; i <= l; i++)
	    	{
	    		for (int j = 1; j <= n; j++)
	    		{
	    			for (int k = 1; k <= m; k++) 
	                {
	            	    cin >> a [i] [j] [k];
	            	    if (a [i] [j] [k] == 'S') sx = i , sy = j , sz = k;
	            	    if (a [i] [j] [k] == 'E') ex = i , ey = j , ez = k;
				    }
				}      
			} 
	        bfs (sx , sy , sz);     
			if (!flag)   
	            printf ("%s\n" , "Trapped!");
	        flag = 0;
	        while (!q.empty())  
	            q.pop();
		} 
		return 0;
}