#!/usr/bin/ruby
#
## https://rosettacode.org/wiki/Cheryl%27s_Birthday
#
struct date(day, month)
var dates = [
    date(15, "May"),
    date(16, "May"),
    date(19, "May"),
    date(17, "June"),
    date(18, "June"),
    date(14, "July"),
    date(16, "July"),
    date(14, "August"),
    date(15, "August"),
    date(17, "August")
]
var filtered = dates.grep {
    dates.grep {
        dates.map{ .day }.count(.day) == 1
    }.map{ .month }.count(.month) != 1
}
var birthday = filtered.grep {
    filtered.map{ .day }.count(.day) == 1
}.group_by{ .month }.values.first_by { .len == 1 }[0]
say "Cheryl's birthday is #{birthday.month} #{birthday.day}."
assert_eq(birthday.day, 16)
assert_eq(birthday.month, "July")