Leetcode: Contains Duplicate II

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 difference between i and j is at most k.

Code (Java):

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public class Solution {     public boolean containsNearbyDuplicate(int[] nums, int k) {         if (nums == null || nums.length <= 1 || k <= 0) {             return false;         }                   Map<Integer, Integer> map = new HashMap<>();                   for (int i = 0; i < nums.length; i++) {             if (map.containsKey(nums[i])) {                 int preIndex = map.get(nums[i]);                 if (i - preIndex <= k) {                     return true;                 } else {                     map.put(nums[i], i);                 }             } else {                 map.put(nums[i], i);             }         }                   return false;     } }

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class Solution {     public boolean containsNearbyDuplicate(int[] nums, int k) {         Set<Integer> hashSet = new HashSet<>();                   for (int i = 0; i < nums.length; i++) {             if (hashSet.contains(nums[i])) {                 return true;             }                           hashSet.add(nums[i]);                           if (hashSet.size() > k) {                 hashSet.remove(nums[i - k]);             }         }                   return false;     } }