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 };
时间： 2024-10-24 10:42:44