算法笔记33：添加与搜索单词 - 数据结构设计

211. 添加与搜索单词 - 数据结构设计

题目需要设计并完成前缀树 (Prefix Tree) 来实现。前缀树就是节点为单词间隔，边为单词字符构成的树。因为单词都是有顺序的，所以从根节点开始走到一个标记为结尾的节点，就可以根据边顺序生成一个字符串。

代码如下：

var Node = function() {
    // store all the children nodes here
    this.children = new Map();
    // need a flag to specify if this is a end of the word
    this.isWord = false;
}

var WordDictionary = function() {
    this.root = new Node();
};

/** 
 * @param {string} word
 * @return {void}
 */
WordDictionary.prototype.addWord = function(word) {
    let p = this.root;
    // iterate through the word
    for (let i = 0; i < word.length; i++) {
        const char = word[i];
        // if current edge is not created before, add it
        if (!p.children.get(char)) {
            p.children.set(char, new Node());
        }
        // bump the pointer
        p = p.children.get(char);
    }
    // set the flag
    p.isWord = true;
};

/** 
 * @param {string} word
 * @return {boolean}
 */
WordDictionary.prototype.search = function(word) {
    const len = word.length;

    const dfs = (node, i) => {
        // if it reaches the end,
        // then the result depend on the flag value
        if (i === len) {
            return node.isWord;
        }


        // if it is '.', we need to check all of its children
        if (word[i] === '.') {
            for (let [char, val] of node.children) {
                if (dfs(val, i + 1)) {
                    return true;
                }
            }
            return false;
        }
        
        // if not, then we do a specific check
        const curr = word[i];
        if (node.children.get(curr)) {
            return dfs(node.children.get(curr), i + 1);
        }
        return false;
    }
    
    // start the search
    return dfs(this.root, 0);
};