Leetcode 219 Contains Duplicate II

Problem:

Given an array of integers and an integer k, find out whether there are two distinct indices i and j in the array such that nums[i] = nums[j] and the absolute difference between i and j is at most k.

Analysis:

This problem has three method.

method 1
naive method. simplify use two for loop to check each pair of Integer.
time complexity O(kn)
space complexity O(1)

method 2
Using HashMap to record <nums[I], I> pairs. when meeting the same number, check whether it satisfies j - I <= k
time complexity O(n)
space complexity O(n)

method3
Using HashSet to check whether the next number is contained in the set which size is k.

public class Solution1 {
	
	
	// sliding window
	 public boolean containsNearbyDuplicate(int[] nums, int k) {
	     
		 TreeSet<Integer> set = new TreeSet<>();
		 for (int i=0; i<nums.length; i++) {
			 if (set.contains(nums[i])) {
				 return true;
			 }else {
				 set.add(nums[i]);
			 }
			 if (i >= k ) {
				 set.remove(nums[i-k]);
			 }			 
		 }		 
		 return false;
	 }	
	 
	 
	 
	 // HashMap
	 public boolean containsNearbyDuplicate1(int[] nums, int k) {
		if (nums == null || nums.length == 0 || k <=0 ) return false;
		
		HashMap<Integer, Integer> map = new HashMap<>();
		for (int i=0; i<nums.length; i++) {
			
			Integer j = map.get(nums[i]);
			if (j != null && i - j <= k) {
				return true;
			}
			map.put(nums[i], i);	
		}
		
		return false;
		
	 }
	 
 
	 
}