class Solution {

    /** T(N) = O(N), O(N) */
    public boolean hasDuplicate(int[] nums) {
        Set<Integer> set = new HashSet<>();
        for(int ele : nums)
            set.add(ele);
        
        // set size won't be same if array has duplicates, because in set we cannot store duplicate elements
        if(set.size() != nums.length)
            return true;
        
        return false;
    }

    /** T(N) = O(N*Log N), O(1) */
    public boolean hasDuplicate(int[] nums) {
        Arrays.sort(nums);
        for(int i=1; i<nums.length; i++)
        {
            if(nums[i-1] == nums[i])
                return true;
        }
        return false;
    }  

    /** T(N) = O(N), O(1) */
    // only if array has positive integers
    public boolean hasDuplicate(int[] nums)
    {
        for(int i=0; i<nums.length-1; i++)
        {
            int diff = Math.abs(nums[i+1] - nums[i]);
            if(diff == 1)
                continue;
            else
                return true;
        }
        return false;
    }
}