Given an array of numbers A, which might contain duplicate elements, How do we find if there are two elements A[i], A[j] such that i, j are distinct and the difference between them is at most k?

duplicates_at_distance.java

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