codeforces 510B. Fox And Two Dots 解题报告

题目链接：http://codeforces.com/problemset/problem/510/B

题目意思：给出 n 行 m 列只有大写字母组成的字符串。问具有相同字母的能否组成一个环。

　　很容易知道要用到深搜。暴力搜索～～～

　　

 #include <iostream>
 #include <cstdio>
 #include <cstdlib>
 #include <cstring>
 using namespace std;

 const int maxn =  + ;
 char g[maxn][maxn];
 bool vis[maxn][maxn];

 int dx[] = {, , , -};
 int dy[] = {, , -, };

 int n, m;

 bool dfs(int x, int y, int px, int py, char c)
 {
     vis[x][y] = ;
     for (int i = ; i < ; i++)    {
         int tx = x + dx[i];
         int ty = y + dy[i];
         if (tx == px && ty == py)    // 和上一次走过的点冲突
             continue;
         if (tx >=  && tx < n && ty >=  && ty < m && g[tx][ty] == c) {
             if (vis[tx][ty])     // 形成环
                 return ;
             if (dfs(tx, ty, x, y, c))
                 return ;
         }
     }
     return ;
 }

 int main()
 {
     while (scanf("%d%d", &n, &m) != EOF) {
         for (int i = ; i < n; i++)
             scanf("%s", g[i]);
         memset(vis, , sizeof(vis));

         bool flag = false;
         for (int i = ; i < n && !flag; i++) {
             for (int j = ; j < m && !flag; j++) {
                 if (!vis[i][j]) {
                     if (dfs(i, j, -, -, g[i][j])) {
                         flag = true;
                         break;
                     }
                 }
             }
         }
         printf("%s\n", flag ? "Yes" : "No");
     }
     return ;
 }

cgy4ever 的代码：

http://ideone.com/udz3bN

 #include <bits/stdc++.h>
 using namespace std;

 int n, m;
 string board[];
 bool visited[][];
 bool findCycle = false;
 int dx[] = {, -, , };
 int dy[] = {, , , -};

 void dfs(int x, int y, int fromX, int fromY, char needColor)
 {
     if(x <  || x >= n || y <  || y >= m) return;
     if(board[x][y] != needColor) return;
     if(visited[x][y])
     {
         findCycle = true;
         return;
     }
     visited[x][y] = true;
     for(int f = ; f < ; f++)
     {
         int nextX = x + dx[f];
         int nextY = y + dy[f];
         if(nextX == fromX && nextY == fromY) continue;
         dfs(nextX, nextY, x, y, needColor);
     }
 }

 int MAIN()
 {
     cin >> n >> m;
     for(int i = ; i < n; i++)
         cin >> board[i];
     memset(visited, false, sizeof(visited));
     for(int i = ; i < n; i++)
         for(int j = ; j < m; j++)
             if(!visited[i][j])
                 dfs(i, j, -, -, board[i][j]);
     cout << (findCycle ? "Yes" : "No") << endl;
     return ;
 }

 int main()
 {
     #ifdef LOCAL_TEST
         freopen("in.txt", "r", stdin);
         freopen("out.txt", "w", stdout);
     #endif
     ios :: sync_with_stdio(false);
     cout << fixed << setprecision();
     return MAIN();
 }