算法：用户喜好--Map与List配合下的查找

package test;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.Scanner;

public class Main6 {
    
    /*
     * 相当于在输入的权值数组的下面，进行序号装入
     * 1 2 3 3 5 -> 
     * 1:1  
     * 2:2 
     * 3:3,4
     * 4:5
     * 入此进行判断范围
     * 
     * 
     * */

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Scanner sc=new Scanner(System.in);
        int n=sc.nextInt();
        HashMap<Integer,ArrayList<Integer>> hm=new HashMap<Integer,ArrayList<Integer>>();
        for(int i=0;i<n;i++) {
            int temp=sc.nextInt();
            if(hm.containsKey(temp)) {
                hm.get(temp).add(i);
            }else {
                ArrayList<Integer> al=new ArrayList<Integer>();
                al.add(i);
                hm.put(temp,al);
            }
             
        }
        
        int m=sc.nextInt();
        int b[]=new int[m];
         
        for(int j=0;j<m;j++) {
            int low=sc.nextInt()-1;
            int high=sc.nextInt()-1;
            int key=sc.nextInt();
            if(!hm.containsKey(key)) {
                b[j]=0;
            }else {
                b[j]=getNum(low, high,hm.get(key));
            }
             
        }
        for(int j=0;j<m;j++) {
            System.out.println(b[j]);
        }
        sc.close();
    }
    public static int getNum(int low ,int high,ArrayList<Integer> al) {
        int i=0;
        int j=al.size()-1;
        //如果list中的最小值比你范围中最大值还大，例如你查找[1,2] 3   
        //显然al.get(3)中最小的也是三，所以里面定然无值，返回0.同理最小值大于它最大值也是返回0.比如2 4 5肯定返回0  
        if(al.get(i)>high || al.get(j)<low ) {
            return 0;
        }else {
            while(al.get(i)<low || al.get(j)>high) {
                if(al.get(i)<low) i++;
                if(al.get(j)>high) j--;
            }
            return j-i+1;
        }
    }
}