#1894

Find the Student that Will Replace the Chalk

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array · binary search · simulation · prefix sum

Description

There are n students in a class numbered from 0 to n - 1. The teacher will give each student a problem starting with the student number 0, then the student number 1, and so on until the teacher reaches the student number n - 1. After that, the teacher will restart the process, starting with the student number 0 again.

You are given a 0-indexed integer array chalk and an integer k. There are initially k pieces of chalk. When the student number i is given a problem to solve, they will use chalk[i] pieces of chalk to solve that problem. However, if the current number of chalk pieces is strictly less than chalk[i], then the student number i will be asked to replace the chalk.

Return the index of the student that will replace the chalk pieces.

Example 1:

Input: chalk = [5,1,5], k = 22

Output: 0

Explanation: The students go in turns as follows:

- Student number 0 uses 5 chalk, so k = 17.

- Student number 1 uses 1 chalk, so k = 16.

- Student number 2 uses 5 chalk, so k = 11.

- Student number 0 uses 5 chalk, so k = 6.

- Student number 1 uses 1 chalk, so k = 5.

- Student number 2 uses 5 chalk, so k = 0.

Student number 0 does not have enough chalk, so they will have to replace it.

Example 2:

Input: chalk = [3,4,1,2], k = 25

Output: 1

Explanation: The students go in turns as follows:

- Student number 0 uses 3 chalk so k = 22.

- Student number 1 uses 4 chalk so k = 18.

- Student number 2 uses 1 chalk so k = 17.

- Student number 3 uses 2 chalk so k = 15.

- Student number 0 uses 3 chalk so k = 12.

- Student number 1 uses 4 chalk so k = 8.

- Student number 2 uses 1 chalk so k = 7.

- Student number 3 uses 2 chalk so k = 5.

- Student number 0 uses 3 chalk so k = 2.

Student number 1 does not have enough chalk, so they will have to replace it.

Solution