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February 15, 2024 07:47
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FizzBuzz-1 in Gleam
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import gleam/io | |
import gleam/int | |
import gleam/float | |
import gleam/list | |
import gleam/set | |
import gleam/result | |
pub fn main() { | |
let list = generate_prime_list(100000) | |
// io.debug(list) | |
io.debug(list.length(list)) | |
} | |
fn cond_val(cond: Bool, true_value: a, false_value: a) -> a { | |
case cond { True -> true_value False -> false_value } | |
} | |
/// range_step(3, 20, 4) -> [3, 7, 11, 15, 19] | |
fn range_step(first: Int, last: Int, step: Int) -> List(Int) { | |
let main = fn () { | |
let last_diff = last - last / step * step | |
let over_count = cond_val(first > last_diff, 1, 0) + int.max({ first - last_diff - 1 } / step, 0) | |
list.range(0, last / step - over_count) | |
|> list.map(fn (i) { i * step + first }) | |
} | |
case first <= last { | |
True -> main() | |
False -> [] | |
} | |
} | |
fn generate_prime_list(n: Int) -> List(Int) { | |
let main = fn () { | |
// [3, 5, 7, 9, 11, 13, 15, 17, 19, 21, ...] (odd numbers >= 3) | |
let root = int.square_root(n) |> result.unwrap(0.0) |> float.truncate | |
let ints = range_step(3, root, 2) | |
// [3, 5, 7, 9, 11, 13, 15, 17, 19, 21, ...] (prime number candidate) | |
let primes = range_step(3, n, 2) |> set.from_list | |
let primes = list.fold(ints, primes, fn (primes, i) { | |
let sub = fn () { | |
// if i == 5 -> [10, 15, 20, 25, 30, ...] (multiple of i) > i | |
let removed_ints = range_step(i * 2, n, i) | |
// sieve of eratosthenes | |
list.fold(removed_ints, primes, fn (primes, k) { | |
// remove the removed_ints from primes | |
set.delete(primes, k) | |
}) | |
} | |
case set.contains(primes, i) { | |
True -> sub() | |
False -> primes | |
} | |
}) | |
// [3, 5, 7, 11, 13, 17, 19, 23, 29, 31, ...] actual primes >= 3 | |
let primes = set.to_list(primes) |> list.sort(int.compare) | |
// add 2 as primes | |
[2, ..primes] | |
} | |
case n { | |
n, if n < 2 -> [] | |
_ -> main() | |
} | |
} |
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