Source code in the coffeescript programming language

startsOnFriday = (month, year) ->
  # 0 is Sunday, 1 is Monday, ... 5 is Friday, 6 is Saturday
  new Date(year, month, 1).getDay() == 5

has31Days = (month, year) ->
  new Date(year, month, 31).getDate() == 31

checkMonths = (year) ->
  month = undefined
  count = 0
  month = 0
  while month < 12
    if startsOnFriday(month, year) and has31Days(month, year)
      count += 1
      console.log year + ' ' + month + ''
    month += 1
  count

fiveWeekends = ->
  startYear = 1900
  endYear = 2100
  year = undefined
  monthTotal = 0
  yearsWithoutFiveWeekends = []
  total = 0
  year = startYear
  while year <= endYear
    monthTotal = checkMonths(year)
    total += monthTotal
    # extra credit
    if monthTotal == 0
      yearsWithoutFiveWeekends.push year
    year += 1
  console.log 'Total number of months: ' + total + ''
  console.log ''
  console.log yearsWithoutFiveWeekends + ''
  console.log 'Years with no five-weekend months: ' + yearsWithoutFiveWeekends.length + ''
  return

fiveWeekends()


1901 2
1902 7
1903 4
1904 0
1904 6
1905 11
1907 2
1908 4
1909 0
1909 9
1910 6
1911 11
1912 2
1913 7
1914 4
1915 0
1915 9
1916 11
1918 2
1919 7
1920 9
1921 6
1922 11
1924 7
..

Total number of months: 201
1900,1906,1917,1923,1928,1934,1945,1951,1956,1962,1973,1979,1984,1990,2001,2007,2012,2018,2029,2035,2040,2046,2057,2063,2068,2074,2085,2091,2096

Years with no five-weekend months: 29