Minimum daily reading pace to finish a textbook

A student must read a textbook of n chapters before an exam. Chapter i has pages[i] pages, and the chapters must be read in order.

The student picks a daily limit x. On each day they read from the current chapter until either the chapter ends or they have read x pages, whichever comes first. A day never continues into the next chapter: if a chapter ends partway through the day, the student stops for that day.

Given pages and the number of days days left before the exam, return the smallest positive integer x that lets the student finish every chapter within days days. Return -1 if no x works.

Implement:

def min_pages_per_day(pages: list[int], days: int) -> int: ...

Constraints

• 1 <= n <= 10^5
• 1 <= pages[i] <= 10^9
• 1 <= days <= 10^9

Example 1

pages = [7, 2, 6], days = 6
output: 3

With x = 3 the student needs 3 + 1 + 2 = 6 days. With x = 2 they need 4 + 1 + 3 = 8 days, which is too many.

Example 2

pages = [4, 9], days = 1
output: -1

Each chapter takes at least one day, so two chapters cannot fit in one day.

Reconstructed from the reported question; details may differ from what interviewers ask.