Leetcode442.java

package com.company;

import java.util.*;

public class Leetcode442 {
    public static void main(String[] args) {
        int arr[]={4,3,2,7,8,2,3,1};
        List<Integer> ans=duplicate(arr);
        System.out.println(ans);
    }


    static List<Integer> duplicate(int[] arr){
        int i=0;
        while(i<arr.length){
            int correctIndex=arr[i]-1;
            if(arr[i]!=arr[correctIndex]){
                swap(arr,i,correctIndex);
            }
            else {
                i++;
            }
        }

        List<Integer> ans=new ArrayList<>();
        for(int j=0;j<arr.length;j++){
            if(arr[j]!=j+1){
                ans.add(arr[j]);
            }
        }

        return ans;
    }

    static void swap(int[] arr, int a, int b){
        int temp=arr[a];
        arr[a]=arr[b];
        arr[b]=temp;
    }
}