[LeetCode] Word Search II

A simple combination of Implement Trie (Prefix Tree) and Word Search. If you've solved them, this problem will become easy :-)

The following code is based on DFS and should be self-explanatory enough. Well, just go ahead and read it. It is long but clear :-)

 1 class TrieNode {
 2 public:
 3     bool isKey;
 4     TrieNode* children[26];
 5     TrieNode() : isKey(false) {
 6         memset(children, NULL, sizeof(TrieNode*) * 26);
 7     }
 8 };
 9 
10 class Trie {
11 public:
12     Trie() {
13         root = new TrieNode();
14     }
15     
16     void add(string& word) {
17         TrieNode* run = root;
18         for (char c : word) {
19             if (!(run -> children[c - 'a']))
20                 run -> children[c - 'a'] = new TrieNode();
21             run = run -> children[c - 'a'];
22         }
23         run -> isKey = true;
24     }
25     
26     bool search(string& word) {
27         TrieNode* p = query(word);
28         return p && p -> isKey;
29     }
30     
31     bool startsWith(string& prefix) {
32         return query(prefix) != NULL;
33     }
34 private:
35     TrieNode* root;
36     TrieNode* query(string& s) {
37         TrieNode* run = root;
38         for (char c : s) {
39             if (!(run -> children[c - 'a'])) return NULL;
40             run = run -> children[c - 'a'];
41         }
42         return run;
43     }
44 };
45 
46 class Solution {
47 public:
48     vector<string> findWords(vector<vector<char>>& board, vector<string>& words) {
49         Trie trie = Trie();
50         for (string word : words) trie.add(word);
51         int m = board.size(), n = board[0].size();
52         for (int r = 0; r < m; r++)
53             for (int c = 0; c < n; c++)
54                 find(trie, board, "", r, c);
55         return vector<string> (st.begin(), st.end());
56     }
57 private:
58     unordered_set<string> st;
59     void find(Trie trie, vector<vector<char>>& board, string word, int r, int c) {
60         int m = board.size(), n = board[0].size();
61         if (board[r][c] == '%') return;
62         word += board[r][c];
63         if (!trie.startsWith(word)) return;
64         if (trie.search(word)) st.insert(word);
65         board[r][c] = '%';
66         if (r) find(trie, board, word, r - 1, c);
67         if (r < m - 1) find(trie, board, word, r + 1, c);
68         if (c) find(trie, board, word, r, c - 1);
69         if (c < n - 1) find(trie, board, word, r, c + 1);
70         board[r][c] = word.back();
71     }
72 };