[leedcode219]Contains Duplicate II

Given an array of integers and an integer k, find out whether there there are two distinct indices i and j in the array such that nums[i] = nums[j] and the difference between i andj is at most k.

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