Leecode no.208 实现Tire(前缀树)

package leecode;

import org.springframework.util.StringUtils;

import java.util.HashMap;
import java.util.Map;

/**
 * Trie（发音类似 "try"）或者说 前缀树 是一种树形数据结构，用于高效地存储和检索字符串数据集中的键。这一数据结构有相当多的应用情景，例如自动补完和拼写检查。
 *
 * 请你实现 Trie 类：
 *
 * Trie() 初始化前缀树对象。
 * void insert(String word) 向前缀树中插入字符串 word 。
 * boolean search(String word) 如果字符串 word 在前缀树中，返回 true（即，在检索之前已经插入）；否则，返回 false 。
 * boolean startsWith(String prefix) 如果之前已经插入的字符串 word 的前缀之一为 prefix ，返回 true ；否则，返回 false 。
 *  
 *
 * 2021/6/1
 */
public class Trie {

    static Map<Character, Integer> characterMap = new HashMap<>();

    static{
        characterMap.put('a', 0);
        characterMap.put('b', 1);
        characterMap.put('c', 2);
        characterMap.put('d', 3);
        characterMap.put('e', 4);
        characterMap.put('f', 5);
        characterMap.put('g', 6);
        characterMap.put('h', 7);
        characterMap.put('i', 8);
        characterMap.put('j', 9);
        characterMap.put('k', 10);
        characterMap.put('l', 11);
        characterMap.put('m', 12);
        characterMap.put('n', 13);
        characterMap.put('o', 14);
        characterMap.put('p', 15);
        characterMap.put('q', 16);
        characterMap.put('r', 17);
        characterMap.put('s', 18);
        characterMap.put('t', 19);
        characterMap.put('u', 20);
        characterMap.put('v', 21);
        characterMap.put('w', 22);
        characterMap.put('x', 23);
        characterMap.put('y', 24);
        characterMap.put('z', 25);
    }

    Trie[] children;

    boolean end = false;

    /** Initialize your data structure here. */
    /**
     * 一个Tile当作一个树的节点
     * children对应当前节点的子节点
     */
    public Trie() {
        children = new Trie[26];
    }

    /** Inserts a word into the trie. */
    public void insert(String word) {
        if(word == null || "".equals(word)){
            this.end = true;
            return;
        }
        char c = word.toCharArray()[0];
        Integer index = characterMap.get(c);
        Trie child = children[index];
        if(child == null){
            children[index] = new Trie();
            child = children[index];
        }
        child.insert(word.substring(1));
    }

    /** Returns if the word is in the trie. */
    public boolean search(String word) {
        if(word == null || "".equals(word)){
            return end;
        }
        char c = word.toCharArray()[0];
        Integer index = characterMap.get(c);
        Trie child = children[index];
        if(child == null){
            return false;
        }
        return child.search(word.substring(1));
    }

    /** Returns if there is any word in the trie that starts with the given prefix. */
    public boolean startsWith(String prefix) {
        if(prefix == null || "".equals(prefix)){
            return true;
        }
        char c = prefix.toCharArray()[0];
        Integer index = characterMap.get(c);
        Trie child = children[index];
        if(child == null){
            return false;
        }
        return child.startsWith(prefix.substring(1));
    }


    public static void main(String[] args) {
        String word = "apple";

        Trie trie = new Trie();
        trie.insert(word);

        boolean search = trie.search("app");
        System.out.println(search);
        boolean startsWith = trie.startsWith("app");
        System.out.println(startsWith);
    }


}