212. 单词搜索 II

 1 class Trie 
 2 {
 3 public:
 4     bool is_end;   //是否以该单词结尾
 5     Trie* son[26]; //该节点儿子的个数
 6     Trie()
 7     {
 8         is_end = false;
 9         for(int i = 0;i < 26;i ++) son[i] = NULL;
10     }
11     
12     /** Inserts a word into the trie. */
13     void insert(string word) 
14     {
15         auto p = this;
16         for(auto c : word) 
17         {
18             int u = c - ‘a‘;
19             if(p->son[u] == NULL) p->son[u] = new Trie();
20             p = p->son[u];
21         }
22         p->is_end = true;
23     }
24     
25     /** Returns if the word is in the trie. */
26     bool search(string word) 
27     {
28         auto p = this;
29         for(auto c : word) 
30         {
31             int u = c - ‘a‘;
32             if(p->son[u] == NULL) return false;
33             p = p->son[u];
34         }
35         return p->is_end;
36     }
37     
38     /** Returns if there is any word in the trie that starts with the given prefix. */
39     bool startsWith(string prefix) 
40     {
41         auto p = this;
42         for(auto c : prefix) 
43         {
44             int u = c - ‘a‘;
45             if(p->son[u] == NULL) return false;
46             p = p->son[u];
47         }
48         return true;
49     }
50 };
51 
52 class Solution 
53 {
54 public:
55     vector<string> res;
56     unordered_set<string> hash;
57     vector<string> findWords(vector<vector<char>>& board, vector<string>& words) 
58     {
59         Trie trie;
60         for(auto a : words) trie.insert(a);
61 
62         int m = board.size();
63         int n = board[0].size();
64         vector<vector<bool>> visited(m,vector<bool>(n,false));
65         for(int i = 0;i < m;i ++)
66         {
67             for(int j = 0;j < n;j ++)
68             {
69                 dfs(board,visited,"",i,j,trie);
70             }
71         }
72         return res;
73     }
74     void dfs(vector<vector<char>>& board,vector<vector<bool>>& visited,string str,int x,int y,Trie trie)
75     {
76         if(x < 0 || x >= board.size() || y < 0 || y >= board[0].size() || visited[x][y]) return;
77         str += board[x][y];
78         if(!trie.startsWith(str)) return;
79         if(trie.search(str) && hash.find(str) == hash.end()) 
80         {
81             res.push_back(str);
82             hash.insert(str);
83         }
84 
85         visited[x][y] = true;
86         dfs(board,visited,str,x - 1,y,trie);
87         dfs(board,visited,str,x + 1,y,trie);
88         dfs(board,visited,str,x,y - 1,trie);
89         dfs(board,visited,str,x,y + 1,trie);
90         visited[x][y] = false;
91     }
92 
93 };