[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;
}
}