Contains Duplicate II

Description:

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 and j is at most k.

Code:

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