# 212. Word Search II

Given an `m x n` `board` of characters and a list of strings `words`, return  all words on the board.

Each word must be constructed from letters of sequentially adjacent cells, where adjacent cells are horizontally or vertically neighboring. The same letter cell may not be used more than once in a word.

Example 1:

``````Input: board = [["o","a","a","n"],["e","t","a","e"],["i","h","k","r"],["i","f","l","v"]], words = ["oath","pea","eat","rain"]
Output: ["eat","oath"]
``````

Example 2:

``````Input: board = [["a","b"],["c","d"]], words = ["abcb"]
Output: []
``````

Constraints:

• `m == board.length`
• `n == board[i].length`
• `1 <= m, n <= 12`
• `board[i][j]` is a lowercase English letter.
• `1 <= words.length <= 3 * 104`
• `1 <= words[i].length <= 10`
• `words[i]` consists of lowercase English letters.
• All the strings of `words` are unique.

``````class Solution {
public:
struct TrieNode {
TrieNode *child[26];
string str;
};
struct Trie {
TrieNode *root;
Trie() : root(new TrieNode()) {}
void insert(string s) {
TrieNode *p = root;
for (auto &a : s) {
int i = a - 'a';
if (!p->child[i]) p->child[i] = new TrieNode();
p = p->child[i];
}
p->str = s;
}
};
vector<string> findWords(vector<vector<char>>& board, vector<string>& words) {
vector<string> res;
if (words.empty() || board.empty() || board[0].empty()) return res;
vector<vector<bool>> visit(board.size(), vector<bool>(board[0].size(), false));
Trie T;
for (auto &a : words) T.insert(a);
for (int i = 0; i < board.size(); ++i) {
for (int j = 0; j < board[i].size(); ++j) {
if (T.root->child[board[i][j] - 'a']) {
search(board, T.root->child[board[i][j] - 'a'], i, j, visit, res);
}
}
}
return res;
}
void search(vector<vector<char>>& board, TrieNode* p, int i, int j, vector<vector<bool>>& visit, vector<string>& res) {
if (!p->str.empty()) {
res.push_back(p->str);
p->str.clear();
}
int d[][2] = {{-1, 0}, {1, 0}, {0, -1}, {0, 1}};
visit[i][j] = true;
for (auto &a : d) {
int nx = a[0] + i, ny = a[1] + j;
if (nx >= 0 && nx < board.size() && ny >= 0 && ny < board[0].size() && !visit[nx][ny] && p->child[board[nx][ny] - 'a']) {
search(board, p->child[board[nx][ny] - 'a'], nx, ny, visit, res);
}
}
visit[i][j] = false;
}
};
``````

Github 同步地址：

https://github.com/grandyang/leetcode/issues/212

Word Search

Unique Paths III

Stream of Characters

Implement Trie (Prefix Tree)

Add and Search Word - Data structure design

https://leetcode.com/problems/word-search-ii/

https://leetcode.com/problems/word-search-ii/discuss/59780/Java-15ms-Easiest-Solution-(100.00)

LeetCode All in One 题目讲解汇总(持续更新中…)

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