217_contains_duplicate.cc

#include <unordered_map>
 
class Solution {
public:
    bool containsDuplicate(vector<int>& nums) {
        std::unordered_map<int, bool> hmap;
        
        for (const int& n : nums) {
            if (hmap.contains(n)) {
                return true;
            }
 
            hmap[n] = true;
        }
 
        return false;
    }
};