DFS Codeforces Round #290 (Div. 2) B. Fox And Two Dots

题目传送门

 /*
     DFS：每个点四处寻找，判断是否与前面的颜色相同，当走到已走过的表示成一个环
 */
 #include <cstdio>
 #include <iostream>
 #include <cstring>
 #include <string>
 #include <map>
 #include <algorithm>
 #include <vector>
 #include <set>
 #include <cmath>
 using namespace std;

 const int MAXN = 1e6 + ;
 const int INF = 0x3f3f3f3f;
 int dx[] = {, -, , };
 int dy[] = {, , , -};
 char a[][];
 int used[][];
 int n, m;

 bool DFS(int x, int y, int px, int py, char ch)
 {
     used[x][y] = ;
     for (int i=; i<=-; ++i)
     {
         int tx = x + dx[i];
         int ty = y + dy[i];
         if (tx == px && ty == py)   continue;
         if (tx >=  && tx <= n- && ty >=  && ty <=m- && a[tx][ty] == ch)
         {
             if (used[tx][ty])   return true;
             if (DFS (tx, ty, x, y, ch)) return true;
         }
     }

     return false;
 }

 int main(void)
 {
     //freopen ("B.in", "r", stdin);

     while (cin >> n >> m)
     {
         memset (used, , sizeof (used));
         for (int i=; i<=n-; ++i)
         {
             scanf ("%s", &a[i]);
         }

         bool flag = false;
         for (int i=; i<=n-; ++i)
         {
             for (int j=; j<=m-; ++j)
             {
                 if (!used[i][j])
                 {
                     if (DFS (i, j, -, -, a[i][j]))
                     {
                         puts ("Yes");   flag = true;    break;
                     }
                 }
             }
             if (flag)   break;
         }

         if (!flag)  puts ("No");
     }

     return ;
 }