Formatted question description: https://leetcode.ca/all/1748.html

# 1748. Sum of Unique Elements

Easy

## Description

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

## Solution

Use a hash map to store each number’s occurrence in nums. Then loop over the hash map and calculate the sum of the elements that occur only once.

class Solution {
public int sumOfUnique(int[] nums) {
Map<Integer, Integer> map = new HashMap<Integer, Integer>();
for (int num : nums) {
int count = map.getOrDefault(num, 0) + 1;
map.put(num, count);
}
int sum = 0;
Set<Integer> set = map.keySet();
for (int num : set) {
int count = map.get(num);
if (count == 1)
sum += num;
}
return sum;
}
}