leetcode-Contains Duplicate II

Difficulty:
Easy
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.

class Solution {
public:
bool containsNearbyDuplicate(vector<int>& nums, int k) {
map<int,int> check;
int size=nums.size();
for(int i=0;i<size;++i){
if(check.find(nums[i])!=check.end()&&i-check[nums[i]]<=k)
return true;
check[nums[i]]=i;
}
return false;
}
};