leetcode: 212. Word Search II

题目来源

• leetcode：212. 单词搜索 II

题目描述

题目解析

前缀和 + DFS

注意：

• 可能出现： hf、 hfks（易错点）

class Solution {
    


    struct TrieNode{
    
        int size;  // 可能出现不止一次
        std::string path;
        std::vector<TrieNode *> children;

        TrieNode() : size(0), children(26, NULL){
    
        }
    };

    void add(TrieNode *root, std::string &word){
    
        TrieNode *node = root;
        for(char ch : word){
    
            int idx = ch - 'a';
            if(node->children[idx] == nullptr){
    
                node->children[idx] = new TrieNode();
            }
            node = node->children[idx];
        }
        node->size ++;
        node->path = word;
    }

    std::set<std::string> set;
    bool process(vector<vector<char>>& board, int i, int j,  TrieNode *node){
    
        int N = board.size(), M = board[0].size();
        if(i < 0 || j < 0 || i == N || j == M || board[i][j] == 0 || node->children[ board[i][j] - 'a'] == nullptr){
    
            return false;
        }

        int idx = board[i][j] - 'a';
        node = node->children[idx];
        if(node->size > 0){
    
            node->size--;  // 易错点......
            set.emplace(node->path);
        }  //可能还没有结束,不能提前返回


        board[i][j] = 0;
        bool ans = false;
        if(process(board, i + 1, j, node)
        || process(board, i - 1, j, node)
        || process(board, i, j + 1, node)
        || process(board, i, j - 1, node)){
    
            ans = true;
        }
        board[i][j] = idx + 'a';
        return ans;
    }
public:
    vector<string> findWords(vector<vector<char>>& board, vector<string>& words) {
    
        TrieNode *root = new TrieNode();
        for(auto w : words){
    
            add(root, w);
        }

        for (int i = 0; i < board.size(); ++i) {
    
            for (int j = 0; j < board[i].size(); ++j) {
    
                TrieNode *node = root;
                process(board, i, j, node);
            }
        }

        return std::vector<std::string> (set.begin(), set.end());
    }
};