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 absolute difference between i and j is at most k.

Solution

public class Solution {
public boolean containsNearbyDuplicate(int[] nums, int k) {
    if(nums==null || nums.length<2 || k==0)
        return false;

    int i=0; 

    HashSet<Integer> set = new HashSet<Integer>();

    for(int j=0; j<nums.length; j++){
        if(!set.add(nums[j])){
            return true;
        }            

        if(set.size()>=k+1){
            set.remove(nums[i++]);
        }
    }

    return false;
}
}