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1748 - Sum of Unique Elements (Easy)

https://leetcode.com/problems/sum-of-unique-elements/

Problem Statement​

You are given an integer array nums. The unique elements of an array are the elements that appear exactly once in the array.

Return the sum of all the unique elements of nums.

Example 1:

Input: nums = [1,2,3,2]
Output: 4
Explanation: The unique elements are [1,3], and the sum is 4.

Example 2:

Input: nums = [1,1,1,1,1]
Output: 0
Explanation: There are no unique elements, and the sum is 0.

Example 3:

Input: nums = [1,2,3,4,5]
Output: 15
Explanation: The unique elements are [1,2,3,4,5], and the sum is 15.

Constraints:

  • 1 <= nums.length <= 100
  • 1 <= nums[i] <= 100

Approach 1: Hash Map​

Written by @wingkwong
class Solution {
public:
    int sumOfUnique(vector<int>& nums) {
        unordered_map<int, int> m;
        int ans = 0;
        // use hash map to count the frequency of each number
        for(int x : nums) m[x]++;
        // unique number would have frequency of 1
        for(auto x : m) {
            if(x.second == 1) {
                ans += x.first;
            }
        }
        return ans;
    }
};