Fix the Bill Splitter

splitBill(totalCents, people) splits a bill in cents between people people. The shares must add up to exactly totalCents, differ by at most one cent, and be listed largest first.

Accounting found that some splits do not add up to the bill. Find the bug and fix it.

Example 1

Input: totalCents = 1000, people = 4
Output: [250, 250, 250, 250]

Example 2

Input: totalCents = 1000, people = 3
Output: [334, 333, 333]
Explanation: The buggy version returns [333, 333, 333]: one cent disappears.

Constraints

1 <= people
0 <= totalCents

The buggy code

function splitBill(totalCents, people) {
  const share = Math.round(totalCents / people);
  return new Array(people).fill(share);
}

function splitBill(totalCents: number, people: number): number[] {
  const share = Math.round(totalCents / people);
  return new Array(people).fill(share);
}

def split_bill(total_cents: int, people: int) -> list[int]:
    share = round(total_cents / people)
    return [share] * people

<?php

function splitBill(int $totalCents, int $people): array
{
    $share = (int) round($totalCents / $people);
    return array_fill(0, $people, $share);
}

class Solution {
    public int[] splitBill(int totalCents, int people) {
        int share = (int) Math.round((double) totalCents / people);
        int[] out = new int[people];
        Arrays.fill(out, share);
        return out;
    }
}

Solution and explanation

Show the bug and the fix

Time O(n) · Space O(n)

The bug: each share is the rounded average, so the shares add up to round(total / n) x n, which is only equal to the total when n divides it. Rounding down loses cents; rounding up invents them.

The fix: give everyone total // n and hand the remainder total % n out one cent at a time to the first remainder people. This is the standard way payment systems allocate money; never split money with floating point and rounding.

Fixed version

function splitBill(totalCents, people) {
  const base = Math.floor(totalCents / people);
  const remainder = totalCents % people; // these people get one extra cent
  return Array.from({ length: people }, (_, i) => base + (i < remainder ? 1 : 0));
}

function splitBill(totalCents: number, people: number): number[] {
  const base = Math.floor(totalCents / people);
  const remainder = totalCents % people; // these people get one extra cent
  return Array.from({ length: people }, (_, i) => base + (i < remainder ? 1 : 0));
}

def split_bill(total_cents: int, people: int) -> list[int]:
    base, remainder = divmod(total_cents, people)  # `remainder` people get one extra cent
    return [base + 1] * remainder + [base] * (people - remainder)

<?php

function splitBill(int $totalCents, int $people): array
{
    $base = intdiv($totalCents, $people);
    $remainder = $totalCents % $people; // these people get one extra cent
    $out = [];
    for ($i = 0; $i < $people; $i++) {
        $out[] = $base + ($i < $remainder ? 1 : 0);
    }
    return $out;
}

class Solution {
    public int[] splitBill(int totalCents, int people) {
        int base = totalCents / people;
        int remainder = totalCents % people; // these people get one extra cent
        int[] out = new int[people];
        for (int i = 0; i < people; i++) out[i] = base + (i < remainder ? 1 : 0);
        return out;
    }
}

Common mistakes

Adding the remainder to the last person only (shares then differ by more than one cent).
Using floats for money at all.

Follow-up questions

Split by weights (60/30/10) without losing cents: the largest remainder method.

Example 1

Example 2

Constraints

The buggy code

Hints

Find and fix the bug

Solution and explanation

Fixed version

Common mistakes

Follow-up questions

Example 1

Example 2

Constraints

The buggy code

Hints

Find and fix the bug

Solution and explanation

Fixed version

Common mistakes

Follow-up questions

More Code Clinic: Find the Bug problems