219. 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.

public class Solution {
    public boolean containsNearbyDuplicate(int[] nums, int k) {
      HashMap<Integer, Integer> map = new HashMap<>();
      for(int i = 0 ; i < nums.length; i++){
          if(map.containsKey(nums[i])){
                if(i - map.get(nums[i]) <= k)
                    return true;
          }
          map.put(nums[i], i);
      }
      return false;
    }
    
    public boolean containsNearbyDuplicate(int[] nums, int k) {   //维护一个 k长的窗口
        Set<Integer> set = new HashSet<>();
        for(int i = 0 ; i < nums.length ; i++){
            if(i > k) set.remove(nums[i - k - 1]);
            if(!set.add(nums[i])) return true;
        }
        return false;
    }
}