[219] 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) {
        //用map存储数组元素和下标，看是否存在与当前元素相等且下标之差小于等于k的元素，存在则返回true；否则将当前元素和其下标存入map。
        Map<Integer,Integer> map=new HashMap<Integer,Integer>();
        if(nums==null||nums.length<=0) return false;
        for(int i=0;i<nums.length;i++){
            if(!map.isEmpty()&&map.containsKey(nums[i])){
                int end=map.get(nums[i]);
                if(i-end<=k) return true;
                else map.put(nums[i],i);
            }else{
                map.put(nums[i],i);
            }
        }
        return false;
    }
}