LC-212. 单词搜索 II

212. 单词搜索 II

给定一个 m x n 二维字符网格 board 和一个单词（字符串）列表 words，找出所有同时在二维网格和字典中出现的单词。

单词必须按照字母顺序，通过 相邻的单元格 内的字母构成，其中“相邻”单元格是那些水平相邻或垂直相邻的单元格。同一个单元格内的字母在一个单词中不允许被重复使用。

示例 1：

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

类似于前缀树,在建树的时候只在叶子结点存储string,每个节点都是map存储26个字符所对应的指针

class Solution {
private:
    set<string> res;
    int m, n;
    struct TreeNode {
        map<char, TreeNode*> child;
        string word;
        TreeNode () {
            word = "";
        }
    };

public:
    void insertTree (TreeNode* root, string word) {
        TreeNode *node = root;
        for (char &k : word) {
	    //这里表示新建节点
            if (!node -> child.count(k)) {
                node -> child[k] = new TreeNode();
            }
            node = node ->child[k];
        }
	//在叶子节点出存储string
        node -> word = word;
    }

    int dir[4][2] = {{1, 0}, {-1, 0}, {0, -1}, {0, 1}};
    void dfs (vector<vector<char>>& board, int i, int j, TreeNode* root) {
        char ch = board[i][j];
        if (!root -> child.count(ch)) {
            return;
        }
	//到达这里就表明存在这个单词的这个字符,而且存储的字符串长度大于0,表示可以生成这个单词
        root = root -> child[ch];
        if (root -> word.size() > 0) {
            res.insert(root -> word);
        }
        board[i][j] = '#';
        for (int k = 0; k < 4; k++) {
            int xx = i + dir[k][0], yy = j + dir[k][1];
            if (xx < 0 || xx >= m || yy < 0 || yy >= n || board[xx][yy] == '#') {

            }else {
                dfs (board, xx, yy, root);
            }
        }
        board[i][j] = ch;
    }
    vector<string> findWords(vector<vector<char>>& board, vector<string>& words) {
        TreeNode *root = new TreeNode();
        for (string &k : words) {
            insertTree(root, k);
        }
        m = board.size(), n = board[0].size();
        for (int i = 0; i < m; i++) {
            for (int j = 0; j < n; j++) {
                dfs(board, i, j, root);
            }
        }
        vector<string> ans(res.begin(), res.end());
        return ans;
    }
};

标签：单词,TreeNode,LC,int,word,II,board,212,root
来源： https://www.cnblogs.com/smilerain/p/15307446.html