Yan Cui
I help clients go faster for less using serverless technologies.
This article is brought to you by
Don’t reinvent the patterns. Catalyst gives you consistent APIs for messaging, data, and workflow with key microservice patterns like circuit-breakers and retries for free.
Problem
You are given the following information, but you may prefer to do some research for yourself.
- 1 Jan 1900 was a Monday.
- Thirty days has September, April, June and November. All the rest have thirty-one, saving February alone, which has twenty-eight, rain or shine. And on leap years, twenty-nine.
- A leap year occurs on any year evenly divisible by 4, but not on a century unless it is divisible by 400.
How many Sundays fell on the first of the month during the twentieth century (1 Jan 1901 to 31 Dec 2000)?
Solution
open System
let ans =
[1901..2000]
|> List.collect (fun y -> [1..12] |> List.map (fun m -> new DateTime(y, m, 1)))
|> List.filter (fun d -> d.DayOfWeek = DayOfWeek.Sunday)
|> List.length
The solution here is simple, for the int list [1901..2000] generates the Cartesian product with the int list [1..12] to get a DateTime object representing the first day in each month from 1901 to 2000, e.g.
From this point, all that’s left is to filter the list of DateTime values to find the ones which represent a Sunday and count them.
Whenever you’re ready, here are 3 ways I can help you:
- Production-Ready Serverless: Join 20+ AWS Heroes & Community Builders and 1000+ other students in levelling up your serverless game. This is your one-stop shop for quickly levelling up your serverless skills.
- I help clients launch product ideas, improve their development processes and upskill their teams. If you’d like to work together, then let’s get in touch.
- Join my community on Discord, ask questions, and join the discussion on all things AWS and Serverless.
open System
let p19 = [for y in 1901..2000 do
for m in 1..12 do yield new DateTime(y,m,1)]
|> List.filter (fun d -> d.DayOfWeek = DayOfWeek.Sunday)
|> List.length