ContainsDuplicate.java

package com.saikat;

public class ContainsDuplicate {
    public static void main(String[] args) {
        int[] nums = {1,2,3,1};
        System.out.println(containsDuplicate(nums));
    }
    static boolean containsDuplicate(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++;
            }
        }

        for(int index = 0; index < arr.length; index++){
            if(arr[index] != index + 1){
                return false;
            }
        }
        return true;
    }

    static void swap(int[] arr, int first, int second){
        int temp = arr[first];
        arr[first] = arr[second];
        arr[second] = temp;
    }
}