Contains Duplicate - LeetCode

Given an array of integers, find if the array contains any duplicates.

Your function should return true if any value appears at least twice in the array, and it should return false if every element is distinct.

Example 1:

Input: [1,2,3,1]
Output: true

Example 2:

Input: [1,2,3,4]
Output: false

Example 3:

Input: [1,1,1,3,3,4,3,2,4,2]
Output: true

Java Solution 1:

class Solution {
    public boolean containsDuplicate(int[] nums) {
        Arrays.sort(nums);
        int k=0;
        for(int i =1;i < nums.length;i++){
            if(nums[i]==nums[k]){
                return true; 
            }
            k++;
        }
        return false;
    }
}

Java Soluton 2:

class Solution {
    public boolean containsDuplicate(int[] nums) {
        if(nums ==null || nums.length == 0)
            return false;
        HashSet<Integer> set = new HashSet<Integer>();
        for(int i : nums){
            if(!set.add(i))
                return true;
        }
        return false;
    }
}

Java Solution 3: