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.

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思路：维持一个规模为k的移动窗口，对于新的元素，只要在移动窗口中可以找到相同的元素就返回true。

 

代码：

1 public class Solution { 2     public boolean containsNearbyDuplicate(int[] nums, int k) { 3         Set
     
       hs = new HashSet
      
       (); 4         for (int i = 0; i < nums.length; ++i) { 5             if (hs.contains(nums[i])) return true; 6             hs.add(nums[i]); 7             if (i >= k) hs.remove(nums[i - k]); 8         } 9         return false;10     }11 }