Introduction

In this blog post, we will explore how to solve the LeetCode problem "1894" using AI. LeetCode is a popular platform for preparing for coding interviews, and with the help of AI tools like Chatmagic, we can generate solutions quickly and efficiently - helping you pass the interviews and get the job offer without having to study for months.

Problem Statement

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. Constraints: chalk.length == n 1 <= n <= 105 1 <= chalk[i] <= 105 1 <= k <= 109

Explanation

Here's the approach and code:

• Key Idea: The problem involves repeated cycles of students using chalk. First calculate the total chalk needed for one complete cycle. Then, reduce k by as many full cycles as possible using the modulo operator (%). Finally, iterate through the students to find the first one who needs to replace the chalk.

• Optimization: Using modulo reduces the number of iterations significantly, especially when k is large.

• Complexity:

  • Runtime Complexity: O(n) - due to the single loop to calculate total chalk and, in the worst case, another loop to find the student who needs to replace the chalk.
  • Storage Complexity: O(1) - constant extra space.

Code

    def chalkReplacer(chalk, k):
    """
    Finds the index of the student who will replace the chalk.

    Args:
        chalk: A list of integers representing the chalk usage of each student.
        k: The initial number of chalk pieces.

    Returns:
        The index of the student who will replace the chalk.
    """
    n = len(chalk)
    total_chalk = sum(chalk)

    k %= total_chalk  # Reduce k to the remaining chalk after full cycles

    for i in range(n):
        if k < chalk[i]:
            return i
        k -= chalk[i]

    return 0  # Should not reach here, but handle edge cases