1. class Solution {
  2.  
  3.     /** T(N) = O(N), O(N) */
  4.     public boolean hasDuplicate(int[] nums) {
  5.         Set<Integer> set = new HashSet<>();
  6.         for(int ele : nums)
  7.             set.add(ele);
  8.  
  9.         // set size won't be same if array has duplicates, because in set we cannot store duplicate elements
  10.         if(set.size() != nums.length)
  11.             return true;
  12.  
  13.         return false;
  14.     }
  15.  
  16.     /** T(N) = O(N*Log N), O(1) */
  17.     public boolean hasDuplicate(int[] nums) {
  18.         Arrays.sort(nums);
  19.         for(int i=1; i<nums.length; i++)
  20.         {
  21.             if(nums[i-1] == nums[i])
  22.                 return true;
  23.         }
  24.         return false;
  25.     }  
  26.  
  27.     /** T(N) = O(N), O(1) */
  28.     // only if array has positive integers
  29.     public boolean hasDuplicate(int[] nums)
  30.     {
  31.         for(int i=0; i<nums.length-1; i++)
  32.         {
  33.             int diff = Math.abs(nums[i+1] - nums[i]);
  34.             if(diff == 1)
  35.                 continue;
  36.             else
  37.                 return true;
  38.         }
  39.         return false;
  40.     }
  41. }