Prefix sum - Swift

class Solution {
    func runningSum(_ nums: [Int]) -> [Int] {
        var pre = [Int]()
        let n = nums.count
        var sum = 0

        for i in nums {
            sum += i
            pre.append(sum)
        }
        return pre
    }
}
public extension Collection {
  func inits<T>(_ transform: (SubSequence) throws -> T) rethrows -> [T] {
    try (0...count).map { try transform(prefix($0)) }
  }

  func inits() -> [SubSequence] {
    inits { $0 }
  }
}

print([1, 7, 14, 9, 11].inits { $0.reduce(0, +) })