219. Contains Duplicate II

HashMap

class Solution {
public:
    bool containsNearbyDuplicate(vector<int>& nums, int k)
    {
        unordered_map<int, int> m;
        for (int i = 0; i < nums.size(); ++i)
        {
            if (i > k && m[nums[i - k - 1]] < i - k + 1)
            {
                m.erase(nums[i - k - 1]);
            }

            if (m.count(nums[i])) return true;
            m[nums[i]] = i;
        }
        return false;
    }
};

• T: $O(n)$
• S: $O(n)$