题解 | #字典树的实现#

import java.util.*;

/**
 * NC124 字典树的实现
 * @author d3y1
 */
public class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     *
     * @param operators string字符串二维数组 the ops
     * @return string字符串一维数组
     */
    public String[] trieU (String[][] operators) {
        List<String> resultList = new ArrayList<>();
        Trie root = new Trie();
        for(String[] op: operators){
            switch(op[0]){
                case "1":{
                    root.insert(op[1]);
                    break;
                }
                case "2":{
                    root.delete(op[1]);
                    break;
                }
                case "3":{
                    boolean found = root.search(op[1]);
                    if(found){
                        resultList.add("YES");
                    }else{
                        resultList.add("NO");
                    }
                    break;
                }
                case "4":{
                    int count = root.prefixNumber(op[1]);
                    resultList.add(String.valueOf(count));
                }
                default:break;
            }
        }

        String[] result = new String[resultList.size()];
        for(int i=0; i<resultList.size(); i++){
            result[i] = resultList.get(i);
        }

        return result;
    }

    /**
     * 字典树Trie
     */
    private class Trie {
        private Trie[] children;
        boolean isEnd;
        private int count;

        public Trie(){
            children = new Trie[26];
            isEnd = false;
            count = 0;
        }

        public void insert(String word){
            Trie curr = this;
            int index;
            for(char ch: word.toCharArray()){
                index = ch - 'a';
                if(curr.children[index] == null){
                    curr.children[index] = new Trie();
                }
                curr = curr.children[index];
                curr.count++;
            }
            curr.isEnd = true;
        }

        public void delete(String word){
            Trie curr = this;
            int index;
            for(char ch: word.toCharArray()){
                index = ch - 'a';
                if(curr.children[index] != null){
                    curr = curr.children[index];
                    curr.count--;
                }
            }
            if(curr.count == 0){
                curr.isEnd = false;
            }
        }

        public boolean search(String word){
            Trie curr = this;
            int index;
            for(char ch: word.toCharArray()){
                index = ch - 'a';
                if(curr.children[index] == null){
                    return false;
                }
                curr = curr.children[index];
            }
            if(!curr.isEnd){
                return false;
            }

            return true;
        }

        public int prefixNumber(String pre){
            Trie curr = this;
            int index;
            for(char ch: pre.toCharArray()){
                index = ch - 'a';
                if(curr.children[index] == null){
                    return 0;
                }
                curr = curr.children[index];
            }

            return curr.count;
        }
    }
}