Java Collections Scenario Based Interview Question

Finding Duplicates in a List

Question: You have a list of integers, and you want to find any duplicates in that list.

Which collection would you use for efficient duplicate detection?

Answer: I would use a HashSet to track seen integers while iterating through the list.

If an integer already exists in the HashSet, it is a duplicate.

Here’s how you could implement this:

package com.example.demo;



import java.util.Arrays;

import java.util.HashSet;

import java.util.List;



public class Test {

 public static void main(String[] args) {

  List<Integer> li = Arrays.asList(12,12,1,2,3,4,2,4);

  HashSet<Integer> hs = new HashSet<>();

  for(Integer i : li) {

   if(hs.contains(i)) {

    System.out.println(i);

   }

   hs.add(i);

  }

 }

}