Problem 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.
Key Insights
- To determine the unique elements, we need to count the occurrences of each element in the array.
- An element is considered unique if it appears exactly once in the array.
- We can utilize a hash table (dictionary) to store the counts of each element efficiently.
- After counting, we can iterate through the hash table to sum the elements that have a count of one.
Space and Time Complexity
Time Complexity: O(n), where n is the number of elements in the array, because we need to traverse the array to count occurrences and then traverse the hash table to sum unique elements.
Space Complexity: O(n), for the hash table that stores the counts of each element.
Solution
To solve this problem, we will use a hash table (or dictionary) to count the occurrences of each number in the array. After counting, we will iterate through the hash table and sum the numbers that have a count of exactly one. This approach ensures that we efficiently find and sum the unique elements.