Add Values That Occur Once

### Problem Return the sum of those values in `nums` that appear exactly once. Values with two or more occurrences contribute nothing. ```cpp class Solution { public: int sumOfUnique(vector<int>& nums); }; ``` ### Examples **Example 1:** ```text nums = [4,2,4,7,2,9] Output: 16 Explanation: Only 7 and 9 appear once. ``` **Example 2:** ```text nums = [6,6,3,3] Output: 0 Explanation: Every value repeats. ``` ### Constraints - `1 <= nums.length <= 100`. - Each value is an integer in `[1,100]`. ### Clarifying Questions Unique means frequency exactly one, rather than one copy of every distinct value. ```hint Inspect the structure Does a repeated value contribute one copy, all copies, or no contribution under the stated definition? ``` ### Reasoning checkpoints - Include a value only when it occurs exactly once in the complete input. - Exclude every repeated value completely. ### Optional extensions How could an incremental sum adjust when a value appears for the second time?