Leetcode: Contains Duplicate II

public class Solution {
    public boolean containsNearbyDuplicate(int[] nums, int k) {
        if (nums == null || nums.length <= 1) {
            return false;
        }
        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;
            }
            map.put(nums[i], i);
        }
        return false;
    }
}