leetcode212

 1 class Solution {
 2     public List<String> findWords(char[][] board, String[] words) {
 3     List<String> res = new ArrayList<>();
 4     TrieNode root = buildTrie(words);
 5     for (int i = 0; i < board.length; i++) {
 6         for (int j = 0; j < board[0].length; j++) {
 7             dfs (board, i, j, root, res);
 8         }
 9     }
10     return res;
11 }
12 
13 public void dfs(char[][] board, int i, int j, TrieNode p, List<String> res) {
14     char c = board[i][j];
15     if (c == ‘#‘ || p.next[c - ‘a‘] == null) return;
16     p = p.next[c - ‘a‘];
17     if (p.word != null) {   // found one
18         res.add(p.word);
19         p.word = null;     // de-duplicate
20     }
21 
22     board[i][j] = ‘#‘;
23     if (i > 0) dfs(board, i - 1, j ,p, res); 
24     if (j > 0) dfs(board, i, j - 1, p, res);
25     if (i < board.length - 1) dfs(board, i + 1, j, p, res); 
26     if (j < board[0].length - 1) dfs(board, i, j + 1, p, res); 
27     board[i][j] = c;
28 }
29 
30 public TrieNode buildTrie(String[] words) {
31     TrieNode root = new TrieNode();
32     for (String w : words) {
33         TrieNode p = root;
34         for (char c : w.toCharArray()) {
35             int i = c - ‘a‘;
36             if (p.next[i] == null) p.next[i] = new TrieNode();
37             p = p.next[i];
38        }
39        p.word = w;
40     }
41     return root;
42 }
43 
44 class TrieNode {
45     TrieNode[] next = new TrieNode[26];
46     String word;
47 }
48 }