Count Evenings Needed to Finish Whole Chapters in Order

A book has chapters with given reading durations in order. Each evening provides a time budget. You may begin a chapter only if you can finish it that evening; unused time does not carry forward. Read chapters in order and read as many whole chapters as fit each evening. Return the number of evenings elapsed when the book is finished. ### Constraints and Clarifications Array values, not array indices, represent durations and time budgets. Use nonnegative integer durations and budgets as a practice domain; no size bounds are reported. An empty book takes zero evenings. If the supplied evening budgets end before the book is complete, return-1 as an explicit interface convention because the report does not specify that case. Do not skip an oversized next chapter to read later ones. ### Example For chapters=[3,2,1] and evenings=[2,5,3,3], return3. The first evening cannot fit chapter1. The second fits the first two chapters, and the third finishes the last chapter. ### What a Strong Answer Covers Maintain the next unread chapter and reset the available time each evening. Count evenings with no progress, handle exact fits, and explain why each chapter is processed at most once. ### Follow-up Questions - Why is it incorrect to subtract an evening's budget from a partially read chapter? - How would the task change if chapters could be split across evenings?