Count Working Days Between Two Dates

Given a start date, an end date (inclusive), and a set of holiday dates, compute the number of working days.

A working day is defined as a date that:

• Is not a Saturday or Sunday.
• Is not present in the provided holiday set.

Input

• startDate: A string in YYYY-MM-DD format.
• endDate: A string in YYYY-MM-DD format. It is guaranteed that endDate >= startDate.
• holidays: A list of distinct date strings, each in YYYY-MM-DD format.

Output

• An integer representing the total number of working days within the [startDate, endDate] range.

Example

Given:

• startDate = 2026-12-24
• endDate = 2026-12-28
• holidays = [2026-12-25]

The dates in the range are:

• 12/24 Thursday (Working day)
• 12/25 Friday (Holiday, not a working day)
• 12/26 Saturday (Weekend, not a working day)
• 12/27 Sunday (Weekend, not a working day)
• 12/28 Monday (Working day)

Output: 2

Constraints

• The date range length (endDate - startDate + 1) can be up to 10^6 days. Design an approach appropriate to this constraint, implying that a naive day-by-day iteration might be too slow.
• The number of holidays can be up to 10^5.