[Quick power, string hash, prefix dictionary tree]

package com.test.autimatic;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

/**
 * @author 25338
 * @version 1.0
 * @date 2021/12/27 14:16
 */
public class PowAndHashString {
    
    

    public static void main(String[] args) {
    
    
        PowAndHashString string = new PowAndHashString();
        System.out.println(string.getPow(3,1));
        //--test
        System.out.println(1e5);
        //--hashString
        string.stringHash("asdfcfdgrasdfcvgfliuoiuliuoiuiwernhchzh",5);
    }

    /**
     * 快速幂
     */
    public int getPow(int p,int time) {
    
    
        int temp = 1;
        while (time > 0){
    
    
            if((time & 1) == 1){
    
    
                temp *= p;
            }
            p *= p;
            time >>= 1;
        }
        return temp;
    }

    /**
     * 字符串hash---中len长度相同的字符有多少个
     */
    public void stringHash(String hash,int len){
    
    
        long[] hashS = new long[hash.length() + 1];
        long[] hashE = new long[hash.length() + 1];
        //解决冲突，散列分布值
        hashS[0] = 1;int mod = 131;
        for (int i = 0; i < hash.length(); i++) {
    
    
            hashS[i + 1] = hashS[i] * mod;
            hashE[i + 1] = hashE[i] * mod + hash.charAt(i);
        }
        //获取元素---
        List<String> result = new ArrayList<>(16);
        Map<Long,Integer> map = new HashMap<>(16);
        for (int i = 1,j = i + len - 1; j < hash.length(); i++, j++) {
    
    
            long key = hashE[j] - hashE[i - 1] * hashS[len];
            Integer val = map.getOrDefault(key, 0);
            if(val == 1){
    
     result.add(hash.substring(i-1,j)); }
            map.put(key,val + 1);
        }
        System.out.println(result);
    }

    /**
     * 字典树
     */
    public static class Trie{
    
    
        public Trie[] children;
        public boolean end;

        public Trie() {
    
    
            children = new Trie[26];
            end = false;
        }

        public Trie(Trie[] children, boolean end) {
    
    
            this.children = children;
            this.end = end;
        }

        /**
         * 插入
         * @param word
         * @return
         */
        public void insert(String word){
    
    
            Trie node = this;
            for (int i = 0; i < word.length(); i++) {
    
    
                if(node.children[word.charAt(i) - 'a'] == null){
    
    
                    node.children[word.charAt(i) - 'a'] = new Trie();
                }
                node = node.children[word.charAt(i) - 'a'];
            }
            node.end = true;
        }

        /**
         * 查找
         * @param temp
         * @return
         */
        public Trie find(String temp){
    
    
            Trie node = this;
            for (int i = 0; i < temp.length(); i++) {
    
    
                if(node.children[temp.charAt(i) - 'a'] == null){
    
    
                    return null;
                }
                node = node.children[temp.charAt(i) - 'a'];
            }
            return node;
        }

        /**
         * 查找结果
         * @param end
         * @return
         */
        public boolean isEnds(String end){
    
    
            Trie trie = find(end);
            return trie != null && trie.end;
        }

        /**
         * 是否以prefix开头
         * @param prefix
         * @return
         */
        public boolean prefis(String prefix){
    
    
            return find(prefix) != null;
        }

    }


}