package com.suai;

import java.math.BigDecimal;
import java.util.ArrayList;
import java.util.Random;

public class Main {

    public static void main(String[] args) {
        ArrayList<Integer> list = new ArrayList<>(150000);
        Random ran = new Random();
        for (int i = 0; i < 150000; i++){
            list.add(ran.nextInt(100));
        }
             System.out.println(list);
        FindNumber f = new FindNumber(list);
        BigDecimal timeStart = new BigDecimal( System.nanoTime());
        int res1 = f.calcOccurenceNum(list, 13, 4);
        BigDecimal nanos = new BigDecimal( System.nanoTime()).subtract(timeStart);
        BigDecimal millis = nanos.divide(new BigDecimal(1000000));
        System.out.println(millis+" ms --- fast");
        System.out.println(res1);
        BigDecimal timeStart2 = new BigDecimal( System.nanoTime());
        int res2 = f.findSlow(13);
        BigDecimal nanos2 = new BigDecimal( System.nanoTime()).subtract(timeStart2);
        BigDecimal millis2 = nanos2.divide(new BigDecimal(1000000));
        System.out.println(millis2+" ms --- slow");
        System.out.println(res2);
    }
}

///////////////////////////////////////// FINDNUMBER.JAVA
package com.suai;
import java.util.ArrayList;

public class FindNumber {
    private ArrayList<Integer> list;

    public FindNumber(ArrayList list){
        this.list = list;
    }

    public int findSlow(int number){
        int res = 0;
        for (int i = 0; i < list.size(); i++){
            if (list.get(i) == number) res++;
        }
        return res;
    }

    public int calcOccurenceNum(ArrayList list, int number, int threadNum){
        int x = list.size() / threadNum;
        int results = 0;
        WorkerThread[] wt = new WorkerThread[threadNum];
        for (int i = 0; i < threadNum; i++){
            wt[i] = new WorkerThread(list, i*x, (((i+1)*x)-1), number);
            wt[i].start();
        }
        try {
            for (int i = 0; i < threadNum; i++) {
                wt[i].join();
                results += wt[i].getResult();
            }
        }
        catch (InterruptedException e) {
            e.printStackTrace();
        }
        return results;
    }

}
/////////////////////////////////////////////////////////WORKERTHREAD.JAVA
package com.suai;
import java.util.ArrayList;

public class WorkerThread extends Thread{
    private ArrayList<Integer> list;
    private int first;
    private int last;
    private int res;
    private int number;

    public WorkerThread(ArrayList x, int first, int last, int number){
        list = x;
        this.first = first;
        this.last = last;
        this.number = number;
    }

    public void run(){
        for (int i = first; i <= last; i++){
            if (list.get(i) == number) res++;
        }
    }

    public int getResult(){
        return res;
    }

}