Word Search II

Description:

Given a matrix of lower alphabets and a dictionary. Find all words in the dictionary that can be found in the matrix. A word can start from any position in the matrix and go left/right/up/down to the adjacent position.

Example

Given matrix:

doaf
agai
dcan

and dictionary:

{"dog", "dad", "dgdg", "can", "again"}

return {"dog", "dad", "can", "again"}

dog:

doaf	
agai
dcan

dad:

doaf	
agai	
dcan

can:

doaf	
agai	
dcan

again:

doaf	
agai	
dcan

Solution:

class Solution {
private:
	struct TrieNode {
		TrieNode* next[26];
		bool flag;
		TrieNode() {
			flag = false;
			fill_n(next, 26, nullptr);
		}
	};

public:
	/**
	 * @param board: A list of lists of character
	 * @param words: A list of string
	 * @return: A list of string
	 */
	vector<string> wordSearchII(vector<vector<char> > &board, vector<string> &words) {
		// write your code here
		vector<string> rc;
		auto m = (int)board.size();
		if (m == 0) return rc;
		auto n = (int)board[0].size();
		if (n == 0) return rc;
		auto sz = (int)words.size();
		auto trie = new TrieNode();
		for (int i = 0; i < sz; ++i) {
			auto word = words[i];
			auto node = trie;
			for (int j = 0; j < word.length(); ++j) {
				if (node->next[word[j]-'a']) {
					node = node->next[word[j]-'a'];
				} else {
					node->next[word[j]-'a'] = new TrieNode();
					node = node->next[word[j]-'a'];
				}
			}
			node->flag = true;
		}
		string tmp;
		for (int i = 0; i < m; ++i) {
			for (int j = 0; j < n; ++j) {
				help(board, m, n, i, j, trie, rc, tmp);
			}
		}
		return rc;
	}

	void help(vector<vector<char>>& board, int m, int n, int i, int j, TrieNode* node, vector<string>& res, string& tmp) {
		if (!node) return;
		if (node->flag) {
			res.push_back(tmp);
			node->flag = false;
		}
		if (i < 0 || i >= m || j < 0 || j >= n) return;
		auto ch = board[i][j];
		if (ch == '*') return;
		board[i][j] = '*';
		tmp.push_back(ch);
		help(board, m, n, i+1, j, node->next[ch-'a'], res, tmp);
		help(board, m, n, i-1, j, node->next[ch-'a'], res, tmp);
		help(board, m, n, i, j+1, node->next[ch-'a'], res, tmp);
		help(board, m, n, i, j-1, node->next[ch-'a'], res, tmp);
		tmp.pop_back();
		board[i][j] = ch;
	}
};