搜索 || BFS || POJ 2157 Maze

#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <queue>
using namespace std;
#define INF 1e9+10
char a[22][22];
int dx[] = {-1, 1, 0, 0};
int dy[] = {0, 0, -1, 1};
int vis[22][22], use[22][22];
int n, m, key[6], num[6], flag;
queue<int> q;
void bfs(int sx, int sy)
{
    while(!q.empty()) q.pop();
    vis[sx][sy] = 1;
    q.push(sx * m + sy);
    int T = 0;
    //队列里是能达到的点，标记vis的是能到达并拓展的点
    while(!q.empty() && T < 400)
    {
        T++;
        int x = q.front() / m, y = q.front() % m; q.pop();
        if(a[x][y] >= ‘A‘ && a[x][y] <= ‘E‘)
        {
            if(key[a[x][y] - ‘A‘] == num[a[x][y] - ‘A‘])//开门
            {
                memset(vis, 0, sizeof(vis));
                a[x][y] = ‘.‘;
                vis[x][y] = 1;
            }
            else//不开门
            {
                q.push(x * m + y);
                continue;
            }
        }
        for(int i = 0; i < 4; i++)
        {
            int xx = x + dx[i], yy = y + dy[i];
            if(xx >= 0 && xx < n && yy >= 0 && yy < m && !vis[xx][yy] && a[xx][yy] != ‘X‘)
            {
                if(a[xx][yy] == ‘G‘) {flag = 1; return;}
                if(a[xx][yy] == ‘.‘)
                {
                    vis[xx][yy] = 1;
                    q.push(xx * m + yy);
                }
                if(a[xx][yy] >= ‘a‘ && a[xx][yy] <= ‘e‘)
                {
                    key[a[xx][yy] - ‘a‘]++;
                    vis[xx][yy] = 1;
                    a[xx][yy] = ‘.‘;
                    q.push(xx * m + yy);
                }
               if(a[xx][yy] >= ‘A‘ && a[xx][yy] <= ‘E‘)
               {
                    q.push(xx * m + yy);//放入队列但不标记
               }
            }
        }
    }
}
int main()
{
    while(1)
    {
        scanf("%d %d", &n, &m);
        if(n == 0 && m == 0) break;
        int sx, sy;
        memset(key, 0, sizeof(key));
        memset(num, 0, sizeof(num));
        memset(vis, 0, sizeof(vis));
        memset(use, 0, sizeof(use));
        for(int i = 0; i < n; i++)
        {
            scanf(" %s", a[i]);
            for(int j = 0; j < m; j++)
            {
                if(a[i][j] == ‘S‘) sx = i, sy = j;
                if(a[i][j] >= ‘a‘ && a[i][j] <= ‘e‘) num[a[i][j] - ‘a‘]++;
            }
        }
        for(int i = 0; i < 5; i++) if(num[i] == 0) num[i] = INF;
        flag = 0;
        bfs(sx, sy);
        if(flag) printf("YES\n");
        else printf("NO\n");
    }
    return 0;
}