Contains Duplicate II

public class Solution {
    public boolean containsNearbyDuplicate(int[] nums, int k) {
        if(nums==null||nums.length<2) return false;
        HashMap<Integer, Integer> hm = new HashMap<Integer, Integer>();
        for(int i=0;i<nums.length;i++){
            if(!hm.containsKey(nums[i])){
                hm.put(nums[i],i);
            }else{
                if(i-hm.get(nums[i])<=k){
                    return true;
                }
            }
        }
        return false;
    }
}