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.
此题和contains duplicate不同之处在于，给定在一个range里面找是否含有重复数字，做法里面就不可以继续用数组排列顺序了，这里面不能打乱顺序，代码如下：
public class Solution {
public boolean containsNearbyDuplicate(int[] nums, int k) {
Set<Integer> set = new HashSet<Integer>();
for(int i=0;i<nums.length;i++){
if(i>=k+1){
set.remove(nums[i-k-1]);
}
if(set.contains(nums[i])){
return true;
}
set.add(nums[i]);
}
return false;
}
}