How should I practice Maximum Number of Balls in a Box?

Start by reading the full statement, solve the visible examples, then compare the pattern against related Roblox phone screen problems in FastPrep.

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FastPrep tags this as a Roblox phone screen coding practice problem when the problem catalog has that company and stage context.

Problem · Hash Table

Maximum Number of Balls in a Box

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Problem statement

You are working in a ball factory where you have n balls numbered from lowLimit up to highLimit inclusive (i.e., n == highLimit - lowLimit + 1), and an infinite number of boxes numbered from 1 to infinity.

Your job is to put each ball in the box whose number equals the sum of the digits of the ball's number. For example, the ball numbered 321 goes in box 3 + 2 + 1 = 6, and the ball numbered 10 goes in box 1 + 0 = 1.

Given two integers lowLimit and highLimit, return the number of balls in the box with the most balls.

Function

countBalls(lowLimit: int, highLimit: int) → int

Examples

Example 1

lowLimit = 1highLimit = 10return = 2

Box 1 receives both ball 1 (digit sum 1) and ball 10 (1+0=1), so the most-filled box has 2 balls.

Example 2

lowLimit = 5highLimit = 15return = 2

Box 6 holds balls 6 and 15 (1+5=6); no other box has more than 1 ball.

Example 3

lowLimit = 19highLimit = 28return = 2

Balls 19 (1+9=10) and 28 (2+8=10) both land in box 10; every other box has 1 ball.

Constraints

1 <= lowLimit <= highLimit <= 10^5