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 a|lone,
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)?



In [13]:

    
let isSunday (d:System.DateTime) = d.DayOfWeek = System.DayOfWeek.Sunday

let dateFromPair (year,month) = new System.DateTime(year, month, 1)

let pairWith lst x = 
    lst |> List.map (fun y -> (x,y)) 

[1901..2000]
|> List.map (pairWith [1..12]) 
|> List.concat
|> List.map dateFromPair
|> List.filter isSunday
|> List.length









    Out[13]:





171



In [ ]: