leetcode - Word Search

最新推荐文章于 2021-07-24 23:29:18 发布

weixin_30654583

最新推荐文章于 2021-07-24 23:29:18 发布

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原文链接：http://www.cnblogs.com/zhanghs/p/3475716.html

本文介绍了一种使用回溯算法在二维字符板上查找指定单词的方法。通过递归地检查每个可能的方向来确定是否存在目标单词，并利用标记数组避免重复访问已检查的字符。

 1 class Solution {
 2 public:
 3     int m, n;
 4     bool search(vector<vector<char> > &board, string & word, int x, int y, vector<vector<bool> >&flag, int off){
 5         if (off == word.size()) return true;
 6         int dx[4] = { -1, 0, 1, 0 };
 7         int dy[4] = { 0, -1, 0, 1 };
 8         for (int i = 0; i < 4; i++){
 9             int xx = x + dx[i];
10             int yy = y + dy[i];
11             if (xx >= 0 && xx < m && yy >= 0 && yy < n && board[xx][yy] == word[off] && !flag[xx][yy]){
12                 flag[xx][yy] = true;
13                 if (search(board, word, xx, yy, flag, off + 1))
14                     return true;
15                 flag[xx][yy] = false;
16             }
17         }
18         return false;
19     }
20     bool exist(vector<vector<char> > &board, string word) {
21         // IMPORTANT: Please reset any member data you declared, as
22         // the same Solution instance will be reused for each test case.
23         if (board.size() == 0 || board[0].size() == 0)
24             return false;
25         m = board.size(), n = board[0].size();
26         int len = word.length();
27         if (len <= 0)
28             return true;
29         vector<vector<bool> >flag = vector<vector<bool> >(m, vector<bool>(n, false));
30         for (int i = 0; i < m; i++){
31             for (int j = 0; j < n; j++){
32                 if (board[i][j] != word[0])
33                     continue;
34                 flag[i][j] = true;
35                 if (search(board, word, i, j, flag, 1)){
36                     return true;
37                 }
38                 flag[i][j] = false;
39             }
40         }
41         return false;
42     }
43 };