Contains Duplicate II

https://leetcode.com/problems/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 iand j is at most k.

解题思路：

简单的新题，在前题 Contains Duplicate 的基础上，用map来记录数字对应的index。遇到map中有的数字就去比较他们的下标，小于等于k就返回true，否则更新下标。

public class Solution {
    public boolean containsNearbyDuplicate(int[] nums, int k) {
        Map<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;
                }
            }
            map.put(nums[i], i);
        }
        return false;
    }
}