Draw K numbers at random (with.Java)

In this article, we’ve been learning about randomly drawing K numbers.

We’ll do this by solving a coding test problem, reflecting on the problem we solved, and exploring other ways to solve it.

Let’s start with the problem.

Problem

You want to create an array of k randomly selected numbers, but you can’t think of a good way to do it, so you decide to randomize the numbers within a certain range and add them to the end of the array if they’ve never been seen before.

Assuming we already know what numbers will be randomized, let’s estimate the actual array of length k that will be created.

You are given an array of integers, arr. Given that the random numbers in the problem will be given in the order they are stored in arr, complete a solution function that returns the resulting array.

However, if the length of the resulting array is less than k, return all the remaining values as -1.

Example input and output

My solution to the problem

import java.util.*;
class Solution {
    public int[] solution(int[] arr, int k) {
        ArrayList<Integer> list = new ArrayList<>();
        int[] answer = new int[k];
        for(int i = 0; i < arr.length; i++){
            if(!list.contains(arr[i])){
                list.add(arr[i]);
            }
            if(list.size() == k){
                break;
            }
        }
        while (list.size() < k) {
            list.add(-1);
        }
        for(int i = 0; i < k; i++){
            answer[i] = list.get(i);
        }
        } return answer;
    }
}

Solution

ArrayList list = new ArrayList<>();: Creates an ArrayList that stores elements of type Integer. This list will be used to remove duplicates and store the result.

int[] answer = new int[k];: Create an array answer to store the result. It is initialized to the size of k.

for(int i = 0; i < arr.length; i++): Starts a loop that iterates over the input array arr, removing duplicates and adding them to list.

if(!list.contains(arr[i])): If list does not contain arr[i] (i.e., it is not a duplicate),

list.add(arr[i]);: adds arr[i] to list.

if(list.size() == k): Terminate the iteration if the size of list is equal to k. In other words, no more duplicates are removed once the desired result size is reached.

while (list.size() < k): If the size of list is less than k,

list.add(-1);: Add -1 to list so that it reaches a size of k.

for(int i = 0; i < k; i++): Start a loop that copies the elements of list into the array answer.

answer[i] = list.get(i);: copy the i-th element of list to the i-th position in answer.

return answer;: Returns the final result, the array answer.

The code removes duplicate values, fills in -1 as needed, and creates and returns the resulting array. The size of the resulting array is equal to or less than k, and it contains only one duplicate value.