20 | 散列表（下）：为什么散列表和链表经常会一起使用

package com.controller.bootweb.demo.dsa;
import java.util.*;
class Headhunter {    String id;    int points;
    public Headhunter(String id, int points) {        this.id = id;        this.points = points;    }}
public class HeadhunterSystem {    private TreeMap<Integer, List<String>> pointsMap; // 通过积分建立索引    private HashMap<String, Headhunter> headhuntersMap; // 通过ID快速查找猎头信息
    public HeadhunterSystem() {        pointsMap = new TreeMap<>();        headhuntersMap = new HashMap<>();    }
    // 添加猎头信息    public void addHeadhunter(String id, int points) {        Headhunter headhunter = new Headhunter(id, points);
        // 更新积分Map        pointsMap.computeIfAbsent(points, k -> new ArrayList<>()).add(id);
        // 更新猎头Map        headhuntersMap.put(id, headhunter);    }
    // 删除猎头信息    public void removeHeadhunter(String id) {        Headhunter headhunter = headhuntersMap.get(id);        if (headhunter != null) {            // 从积分Map中移除            pointsMap.get(headhunter.points).remove(id);
            // 从猎头Map中移除            headhuntersMap.remove(id);        }    }
    // 更新猎头积分    public void updatePoints(String id, int newPoints) {        removeHeadhunter(id); // 先移除再重新添加        addHeadhunter(id, newPoints);    }
    // 查找积分在某个区间的猎头ID列表    public List<String> findHeadhuntersInPointsRange(int start, int end) {        List<String> result = new ArrayList<>();
        // 使用 TreeMap 的 subMap 方法找到积分区间的子集        NavigableMap<Integer, List<String>> subMap = pointsMap.subMap(start, true, end, true);
        // 合并子集中的所有ID        for (List<String> ids : subMap.values()) {            result.addAll(ids);        }
        return result;    }
    // 查找按照积分从小到大排名在第x位到第y位之间的猎头ID列表    public List<String> findHeadhuntersByRank(int x, int y) {        List<String> result = new ArrayList<>();
        // 遍历积分Map，记录排名        int currentRank = 1;        for (List<String> ids : pointsMap.values()) {            for (String id : ids) {                if (currentRank >= x && currentRank <= y) {                    result.add(id);                }                currentRank++;            }        }
        return result;    }
    public List<String> findHeadhuntersByRankOptimized(int x, int y) {        List<String> result = new ArrayList<>();        int currentRank = 1;
        for (List<String> ids : pointsMap.values()) {            for (String id : ids) {                if (currentRank > y) {                    // 已经超过排名范围，结束遍历                    return result;                }
                if (currentRank >= x) {                    // 在排名范围内，添加到结果列表                    result.add(id);                }
                currentRank++;            }        }
        return result;    }

    // 根据ID查找猎头信息    public Headhunter findHeadhunterById(String id) {        return headhuntersMap.get(id);    }
    // 获取所有猎头ID    public Iterable<String> getAllHeadhunters() {        return headhuntersMap.keySet();    }
    // 获取所有积分信息    public Iterable<Integer> getAllPoints() {        return pointsMap.keySet();    }}

package com.controller.bootweb.demo.dsa;
import java.util.List;
public class TestHeadhunterSystem {    public static void main(String[] args) {        HeadhunterSystem headhunterSystem = new HeadhunterSystem();
        // 添加猎头信息        headhunterSystem.addHeadhunter("hunter1", 100);        headhunterSystem.addHeadhunter("hunter2", 150);        headhunterSystem.addHeadhunter("hunter3", 120);        headhunterSystem.addHeadhunter("hunter4", 180);        headhunterSystem.addHeadhunter("hunter5", 90);
        // 打印所有猎头ID和积分        System.out.println("All Headhunters:");        for (String id : headhunterSystem.getAllHeadhunters()) {            System.out.println("ID: " + id + ", Points: " + headhunterSystem.findHeadhunterById(id).points);        }
        // 查找积分在某个区间的猎头ID列表        int startRange = 100;        int endRange = 150;        List<String> headhuntersInRange = headhunterSystem.findHeadhuntersInPointsRange(startRange, endRange);        System.out.println("\nHeadhunters in Points Range (" + startRange + " to " + endRange + "):");        System.out.println(headhuntersInRange);
        // 查找按照积分从小到大排名在第x位到第y位之间的猎头ID列表        int rankX = 2;        int rankY = 4;        List<String> headhuntersByRank = headhunterSystem.findHeadhuntersByRankOptimized(rankX, rankY);        System.out.println("\nHeadhunters by Rank (" + rankX + " to " + rankY + "):");        System.out.println(headhuntersByRank);    }}