1748. Sum of Unique Elements

O(n) time O(n) space

class Solution {
public:
    int sumOfUnique(vector<int>& nums) {
        unordered_map<int, int> m;
        for (int x : nums) {
            ++m[x];
        }
        int res = 0;
        for (auto &[x, cnt] : m) {
            if (cnt == 1) {
                res += x;
            }
        }
        return res;
    }
};