sums-of-parts.md

Sums of Parts ^{6 Kyu}

^{LINK TO THE KATA - FUNDAMENTALS PERFORMANCE ALGORITHMS}

Description

Let us consider this example (array written in general format):

ls = [0, 1, 3, 6, 10]

Its following parts:

ls = [0, 1, 3, 6, 10]
ls = [1, 3, 6, 10]
ls = [3, 6, 10]
ls = [6, 10]
ls = [10]
ls = []

The corresponding sums are (put together in a list): [20, 20, 19, 16, 10, 0]

The function parts_sums (or its variants in other languages) will take as parameter a list ls and return a list of the sums of its parts as defined above.

Other Examples:

ls = [1, 2, 3, 4, 5, 6]
parts_sums(ls) -> [21, 20, 18, 15, 11, 6, 0]

ls = [744125, 935, 407, 454, 430, 90, 144, 6710213, 889, 810, 2579358]
parts_sums(ls) -> [10037855, 9293730, 9292795, 9292388, 9291934, 9291504, 9291414, 9291270, 2581057, 2580168, 2579358, 0]

Notes

• Take a look at performance: some lists have thousands of elements.
• Please ask before translating.

Solution

const partsSums = ls => {
  let sum = ls.reduce((acc, curr) => acc + curr, 0)

  const result = [sum]

  for (let i = 0; i < ls.length; i++) {
    sum -= ls[i]

    result.push(sum)
  }

  return result
}