class Solution {
public:

    struct TrieNode
    {
        TrieNode *child[26];
        string node;
        TrieNode():node("")
        {
            for(auto &a:child)
                a=NULL;
        }
    };
    struct Trie
    {
        TrieNode *root;
        Trie():root(new TrieNode()){}
        void
 
 insert(string s)
        {
            TrieNode *p=root;
            for(auto &str:s)
            {
                int i=str-'a';
                if(!p->child[i])
                {
                    p->child[i]=new TrieNode();

                }
                p=p->child[i];
            }
            p->node =s;
        }

    };
    vector<string> findWords(vector<vector<char
 
>>& board, vector<string>& words) {

        vector<string> result;
        if(board.empty()||board[0].empty()||words.empty())
            return result;

        vector<vector<bool>> dp(board.size(),vector<bool>(board[0].size(),false));
        Trie T;
        for
 
(auto &s:words)
            T.insert(s);

        for(int i=0;i<board.size();i++)
        {
            for(int j=0;j<board[0].size();j++)
            {
                if(T.root->child[board[i][j]-'a'])
                {
                    dp[i][j]=true;//表示當前 節點 已經走過
                    WordSearch(board,T.root->child[board[i][j]-'a'],i,j,dp,result);
                    dp[i][j]=false;//去掉走過的痕跡
                }
            }
        }

        return result;
    }

    void WordSearch(vector<vector<char>>& board,TrieNode *p,int i,int j,vector<vector<bool>> &dp,vector<string> &result)
    {
        if(!p->node.empty())//如果當前字典樹位於Node處，表示有單詞,找到一次，將該單詞處的標記清除，繼續往下找
        {
            result.push_back(p->node);
            p->node.clear();
        }
        int  direction[4][2]={-1,0,0,1,1,0,0,-1};//定義四個方向

       for(int k=0;k<4;k++)
       {
           int new_i=i+direction[k][0];  //新的i
           int new_j=j+direction[k][1]; //新的j

           //跟上面同樣的思想，把新的節點看成當前節點繼續往前查詢
           if(new_i>=0&&new_i<board.size()&&new_j>=0&&new_j<board[0].size()&&dp[new_i][new_j]==false&&p->child[board[new_i][new_j]-'a'])
           {
               dp[new_i][new_j]=true;
               WordSearch(board,p->child[board[new_i][new_j]-'a'],new_i,new_j,dp,result);
               dp[new_i][new_j]=false;
           }
       }
    }
};