< Back 1748. Sum of Unique Elements Given an array of integers, only sum the ones that appear once. Use a Counter from the collections module to count occurrences. Use list comprehension to retain unique numbers - sum the list. The solution is as follows: from collections import Counter class Solution: def sumOfUnique(self, nums: List[int]) -> int: counts = Counter(nums) return sum([num for num in counts if counts[num] < 2]) _ Time Complexity: O(n) - We iterate through the array to count all the integers. _ Space Complexity: O(n) - We store the count of each interger.