local fmt = require "fmt"

local dates = {}
local years = {}
for y = 1900, 2100 do
    local has_five = false
    for m = 1, 12 do
        local fri = 0
        local sat = 0
        local sun = 0
        for d = 1, fmt.month(m, y) do
            local t = os.time({year = y, month = m, day = d})
            local dow = tonumber(os.date("%u", t))
            if dow == 5 then
                fri += 1
            elseif dow == 6 then
                sat += 1
            elseif dow == 7 then
                sun += 1
            end
        end
        local fd = os.date("%b - %Y", os.time({year = y, month = m, day = 1}))
        if fri == 5 and sat == 5 and sun == 5 then
            dates:insert(fd)
            has_five = true
        end
    end
    if !has_five then years:insert(y) end
end

print("Between 1900 and 2100:-")
print($"  There are {#dates} months that have five full weekends.")
print("  The first 5 are:")
for i = 1, 5 do print($"    {dates[i]}") end
print("  and the last 5 are:")
for i = -4, 0 do print($"    {dates[#dates + i]}") end
print($"\n  There are {#years} years that do not have at least one five-weekend month, namely:")
fmt.tprint("  %d", years, 10)