Raúl Pera

In this problem, we will receive an array of numbers, and we must return an array where every number is the sum of it previously numbers.

Input: nums = [1,2,3,4]
Output: [1,3,6,10]
Explanation: Running sum is obtained as follows: [1, 1+2, 1+2+3, 1+2+3+4].

To approach this problem, we will use an auxiliar variable to store the sum of every passed number in the loop.

var sum = 0

1. We will loop over the given array, at same time we will make a new array using map function
2. Updating the auxiliar variable with the sum of its value and every new element
3. Getting the auxiliar value

class Solution {
    func runningSum(_ nums: [Int]) -> [Int] {
        var sum = 0         // Auxiliar variable
        return nums.map {   // 1. Map function. Iterate over array and apply transformer for every element
            sum += $0       // 2. Updating auxiliar variable
            return sum      // 3. Get sum value to the looped element
        }
    }
}

Time complexity: O(n)
Due we only loop every element of the given array

Space complexity: O(1)
Due we are creating a variable to update the sum value