LeetCode #219 - 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 absolute difference between i and j is at most k.

Example 1:

Input: nums = [1,2,3,1], k = 3
Output: true

Example 2:

Input: nums = [1,0,1,1], k = 1
Output: true

Example 3:

Input: nums = [1,2,3,1,2,3], k = 2
Output: false

对于一个数组判断是否存在两个元素数值相等，而且下标相差不超过k，还是利用哈希表记录数值上一次出现的下标，当这个数值再次出现进行比较即可。

class Solution {
public:
    bool containsNearbyDuplicate(vector<int>& nums, int k) {
        unordered_map<int,int> hash;
        for(int i=0;i<nums.size();i++)
        {
            if(hash.count(nums[i])==0) hash[nums[i]]=i;
            else
            {
                if(i-hash[nums[i]]<=k) return true;
                else hash[nums[i]]=i;
            }
        }
        return false;
    }
};