217. Contains Duplicate

Given an integer array nums, return true if any value appears at least twice in the array, and return false if every element is distinct.

Example 1:

Input: nums = [1,2,3,1]

Output: true

Explanation:

The element 1 occurs at the indices 0 and 3.

Constraints:

• 1 <= nums.length <= 10^5

• -10^9<= nums[i] <= 10^9

Solutions-

public static void main(String[] args) {

            int[] arr = {1,2,4,1,5,6};

            System.out.println(containsduplicate1(arr));
            System.out.println(containsduplicate2(arr));
            System.out.println(containsduplicate3(arr));
            System.out.println(containsduplicate4(arr));

   }

public static boolean containsduplicate1(int[] arr) {

    //BruteForcing our way with looping in an array for each element
    //Time complexity - O(n^2)

    int len = arr.length;

    for(int i=0 ; i<len-1 ; i++ )
     for(int j = i+1 ; j< len ; j++) {

        if(arr[i] == arr[j]) 
                    return true; 
        }

    return false;
}

public static boolean containsduplicate2(int[] arr) {

        //Using Set we add every element in a set which has the property to only store unique
        //numbers and have a method to directly  check  if  set contains the number.
        //Time Complexity - O(1) for set method and O(n) for looping once --> O(n)

        Set<Integer> set1 = new HashSet<>();

        for(int x: arr) {
           if(set1.contains(x))
                return true;
            else 
                set1.add(x); 
        }

    return false; 
}

public static boolean containsduplicate3(int[] arr ) {

        // using Java 8 Stream API , One line solution to showcase API stream knowledge
        //Time Complexity - O(n)

        return Arrays.stream(arr).distinct().count() < arr.length; 
    }

public static boolean containsduplicate4(int[] arr) {

        //using sort
        //Time Complexity - O(nlogn)

        Arrays.sort(arr);  // Time - 0(nlogn) ( Dual-Pivot Quicksort ) 

        for(int i =1 ; i< arr.length ;i++)  
                if(arr[i] == arr[i-1])
                            return true;

            return false; 
}