DFS/BFS Codeforces Round #301 (Div. 2) C. Ice Cave

题目传送门

 /*
     题意：告诉起点终点，踩一次, '.'变成'X'，再踩一次，冰块破碎，问是否能使终点冰破碎
     DFS：如题解所说，分三种情况：1. 如果两点重合，只要往外走一步再走回来就行了；2. 若两点相邻，
         那么要不就是踩一脚就破了或者踩一脚走开再走回来踩一脚破了；3. 普通的搜索看是否能到达，
         若能还是要讨论终点踩几脚的问题:)
     DFS 耗时大，险些超时，可以用BFS来做
 */
 #include <cstdio>
 #include <algorithm>
 #include <cstring>
 #include <string>
 #include <iostream>
 using namespace std;

 const int MAXN = 5e2 + ;
 const int INF = 0x3f3f3f3f;
 int n, m;
 int sx, sy, ex, ey;
 char maze[MAXN][MAXN];
 bool vis[MAXN][MAXN];
 int dx[] = {, -, , };
 int dy[] = {, , -, };

 void DFS(int x, int y)
 {
     vis[x][y] = true;
     if (maze[x][y] == 'X')    return ;

     for (int i=; i<; ++i)
     {
         int tx = x + dx[i];
         int ty = y + dy[i];

         if (tx <= n && tx >=  && ty <= m && ty >=  && !vis[tx][ty])
         {
             DFS (tx, ty);
         }
     }

     return ;
 }

 int main(void)        //Codeforces Round #301 (Div. 2) C. Ice Cave
 {
     //freopen ("C.in", "r", stdin);

     while (scanf ("%d%d", &n, &m) == )
     {
         memset (vis, , sizeof (vis));
         for (int i=; i<=n; ++i)
         {
             scanf ("%s", maze[i]+);
         }
         scanf ("%d%d", &sx, &sy);
         scanf ("%d%d", &ex, &ey);

         int cnt = ;    bool flag = false;
         for (int i=; i<; ++i)
         {
             int tx = ex + dx[i];
             int ty = ey + dy[i];
             if (tx == sx && ty == sy)    flag = true;
             if (tx <= n && tx >=  && ty <= m && ty >=  && maze[tx][ty] == '.')    cnt++;
         }

         if (sx == ex && sy == ey)
         {
             if (cnt >= )    puts ("YES");
             else puts ("NO");
         }
         else if (flag)
         {
             if (maze[ex][ey] == 'X')    puts ("YES");
             else
             {
                 if (cnt >= )    puts ("YES");
                 else    puts ("NO");
             }
         }
         else
         {
             maze[sx][sy] = '.';
             DFS (sx, sy);
             if (vis[ex][ey])
             {
                 if (maze[ex][ey] == 'X')    puts ("YES");
                 else if (cnt >= )    puts ("YES");
                 else    puts ("NO");
             }
             else    puts ("NO");
         }
     }

     return ;
 }

 #include <cstdio>
 #include <algorithm>
 #include <cstring>
 #include <queue>
 #include <string>
 #include <iostream>
 using namespace std;

 const int MAXN = 5e2 + ;
 const int INF = 0x3f3f3f3f;
 int n, m;
 int sx, sy, ex, ey;
 char maze[MAXN][MAXN];
 bool vis[MAXN][MAXN];
 int dx[] = {, -, , };
 int dy[] = {, , -, };

 bool BFS(void)
 {
     queue<pair<int, int> > Q;
     Q.push (make_pair (sx, sy));

     while (!Q.empty ())
     {
         int x = Q.front ().first;    int y = Q.front ().second;    Q.pop ();
         for (int i=; i<; ++i)
         {
             int tx = x + dx[i];
             int ty = y + dy[i];

             if (tx == ex && ty == ey)    return true;

             if (tx <= n && tx >=  && ty <= m && ty >=  && maze[tx][ty] == '.')
             {
                 maze[tx][ty] = 'X';
                 Q.push (make_pair (tx, ty));
             }
         }
     }

     return false;
 }

 int main(void)        //Codeforces Round #301 (Div. 2) C. Ice Cave
 {
     //freopen ("C.in", "r", stdin);

     while (scanf ("%d%d", &n, &m) == )
     {
         memset (vis, , sizeof (vis));
         for (int i=; i<=n; ++i)
         {
             scanf ("%s", maze[i]+);
         }
         scanf ("%d%d", &sx, &sy);
         scanf ("%d%d", &ex, &ey);

         int cnt = ;    bool flag = false;
         for (int i=; i<; ++i)
         {
             int tx = ex + dx[i];
             int ty = ey + dy[i];
             if (tx == sx && ty == sy)    flag = true;
             if (tx <= n && tx >=  && ty <= m && ty >=  && maze[tx][ty] == '.')    cnt++;
         }

         if (sx == ex && sy == ey)
         {
             if (cnt >= )    puts ("YES");
             else puts ("NO");
         }
         else if (flag)
         {
             if (maze[ex][ey] == 'X')    puts ("YES");
             else
             {
                 if (cnt >= )    puts ("YES");
                 else    puts ("NO");
             }
         }
         else
         {
             maze[sx][sy] = '.';
             //DFS (sx, sy);
             if (BFS () == true)
             {
                 if (maze[ex][ey] == 'X')    puts ("YES");
                 else if (cnt >= )    puts ("YES");
                 else    puts ("NO");
             }
             else    puts ("NO");
         }
     }

     return ;
 }

BFS做法