BFS+贪心 HDOJ 5335 Walk Out

题目传送门

 /*
     题意：求从(1, 1)走到(n, m)的二进制路径值最小
     BFS+贪心：按照标程的作法，首先BFS搜索所有相邻0的位置，直到1出现。接下去从最靠近终点的1开始，
             每一次走一步，不走回头路，只往下或往右走。因为满足i = j + (i - j)的坐标(j, i - j)可能不止一个，选择最小的访问
 */
 #include <cstdio>
 #include <algorithm>
 #include <cstring>
 #include <cmath>
 #include <queue>
 #include <vector>
 using namespace std;

 const int MAXN = 1e3 + ;
 const int INF = 0x3f3f3f3f;
 int dx[] = {, , , -};
 int dy[] = {, , -, };
 char maze[MAXN][MAXN];
 bool vis[MAXN][MAXN];
 int n, m;

 bool judge(int x, int y)    {
     if (x <  || x > n || y <  || y > m || vis[x][y]) return false;
     return true;
 }

 void BFS(void)  {
     memset (vis, false, sizeof (vis));  int mx = ;
     queue<pair<int, int> > Q;   Q.push (make_pair (, ));  vis[][] = true;
     while (!Q.empty ()) {
         int x = Q.front ().first, y = Q.front ().second; Q.pop ();
         if (maze[x][y] == '')  {
             for (int i=; i<; ++i) {
                 int tx = x + dx[i], ty = y + dy[i];
                 if (!judge (tx, ty))    continue;
                 mx = max (mx, tx + ty);
                 Q.push(make_pair (tx, ty));    vis[tx][ty] = true;
             }
         }
     }

     if (vis[n][m] && maze[n][m] == '') {
         puts (""); return ;
     }

     printf ("");
     for (int i=mx; i<n+m; ++i) {
         char mn = '';
         for (int j=; j<=n; ++j)    {
             if ( <= i - j && i - j <= m && vis[j][i-j])    {
                 mn = min (mn, maze[j+][i-j]);
                 mn = min (mn, maze[j][i-j+]);
             }
         }
         printf ("%c", mn);
         for (int j=; j<=n; ++j)    {
             if ( <= i - j && i - j <= m && vis[j][i-j])    {
                 if (maze[j+][i-j] == mn) vis[j+][i-j] = true;
                 if (maze[j][i-j+] == mn) vis[j][i-j+] = true;
             }
         }
     }
     puts ("");
 }

 int main(void)  {       //HDOJ 5335 Walk Out
     //freopen ("I.in", "r", stdin);
     int T;  scanf ("%d", &T);
     while (T--) {
         scanf ("%d%d", &n, &m);
         for (int i=; i<=n; ++i) scanf ("%s", maze[i] + );
         for (int i=; i<=n; ++i)  maze[i][] = maze[i][m+] = '';
         for (int i=; i<=m+; ++i)  maze[][i] = maze[n+][i] = '';
         BFS ();
     }

     return ;
 }