import java.util.HashMap;

public class Solution {
    public boolean containsNearbyDuplicate(int[] nums, int k) {
        HashMap<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;
    }
}

map是一个接口

而hashmap是它的一种实现方式

for  this problem, if you use eclipse,you will find that we need a () after the fucthion “new”;

another should be pay attention is when I use eclipse as the edcitior and I found that map.get()’s para is key.

So we should put the array as <num[i],i>in the hash map we defined.

here is the code.