[JavaScript 刷题] 树 - 实现前缀树, leetcode 208

[JavaScript 刷题] 树 - 实现前缀树, leetcode 208

github repo 地址: https://github.com/GoldenaArcher/js_leetcode，Github 的目录 大概 会更新的更勤快一些。

题目地址：208. Implement Trie (Prefix Tree)

题目

如下：

A trie (pronounced as “try”) or prefix tree is a tree data structure used to efficiently store and retrieve keys in a dataset of strings. There are various applications of this data structure, such as autocomplete and spellchecker.

Implement the Trie class:

• Trie() Initializes the trie object.
• void insert(String word) Inserts the string word into the trie.
• boolean search(String word) Returns true if the string word is in the trie (i.e., was inserted before), and false otherwise.
• boolean startsWith(String prefix) Returns true if there is a previously inserted string word that has the prefix prefix, and false otherwise.

解题思路

前缀树 trie 中讲了一下 trie 的一点儿应用场景以及基础实现，这里对于 trie 的实现会使用 前缀树 trie 中的。

insert， search 和 startsWith 基本逻辑都是遍历 trie。

insert 在遍历中将该单词添加到 trie 中。

search 和 startsWith 的逻辑基本完全一致，唯一有区别的就是返回值。search 返回当前搜索的单词是否存在于 trie 中，即在结束的时候，这个节点必须是一个单词的结尾。startsWith 只要判断该前缀是否存在于 trie 中即可。

使用 JavaScript 解题

class TrieNode {
    
    
  constructor(val) {
    
    
    this.val = val;
    this.children = [];
    this.isWord = false;
  }

  getIdx(ch) {
    
    
    return ch.charCodeAt(0) - "a".charCodeAt(0);
  }

  hasChild(ch) {
    
    
    return this.children[this.getIdx(ch)] !== undefined;
  }

  createChild(ch) {
    
    
    this.children[this.getIdx(ch)] = new TrieNode(ch);
  }

  getChild(ch) {
    
    
    return this.children[this.getIdx(ch)];
  }
}

var Trie = function () {
    
    
  this.trie = new TrieNode("");
};

/**
 * @param {string} word
 * @return {void}
 */
Trie.prototype.insert = function (word) {
    
    
  let root = this.trie;
  for (const ch of word) {
    
    
    if (root.hasChild(ch));
    else root.createChild(ch);

    root = root.getChild(ch);
  }

  root.isWord = true;
};

/**
 * @param {string} word
 * @return {boolean}
 */
Trie.prototype.search = function (word) {
    
    
  let root = this.trie;
  for (const ch of word) {
    
    
    if (!root.hasChild(ch)) return false;
    root = root.getChild(ch);
  }
  return root.isWord;
};

/**
 * @param {string} prefix
 * @return {boolean}
 */
Trie.prototype.startsWith = function (prefix) {
    
    
  let root = this.trie;
  for (const ch of prefix) {
    
    
    if (!root.hasChild(ch)) return false;
    root = root.getChild(ch);
  }

  return true;
};