Contains Duplicate II

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

这里用HashMap。很简单，代码如下：

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])){            if(i-map.get(nums[i])<=k)                return true;        }        //这里向map中存的已经是离它最近的数了        map.put(nums[i],i);    }    return false;}