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pub fn shortscale(num: u64) -> String {
if num <= 20 || num > 999_999_999_999_999_999 {
return String::from(map(num));
}
let vec = [
jillions(num, 1_000_000_000_000_000),
jillions(num, 1_000_000_000_000),
jillions(num, 1_000_000_000),
jillions(num, 1_000_000),
jillions(num, 1_000),
hundreds(num),
]
.concat();
let vec = concat_and(vec, tens_and_units(num));
vec.join(" ")
}
type Strvec = Vec<&'static str>;
fn lookup(num: u64) -> Strvec {
match num {
0 => vec![],
_ => vec![map(num)],
}
}
fn tens_and_units(num: u64) -> Strvec {
let num = num % 100;
match num {
0..=20 => lookup(num),
_ => [lookup(num / 10 * 10), lookup(num % 10)].concat(),
}
}
fn hundreds(num: u64) -> Strvec {
let num = num % 1000 / 100;
match num {
0 => vec![],
_ => [lookup(num), lookup(100)].concat(),
}
}
fn jillions(num: u64, scale: u64) -> Strvec {
let num = num % (scale * 1000) / scale;
match num {
0 => vec![],
_ => [one_to_999(num), lookup(scale)].concat(),
}
}
fn one_to_999(num: u64) -> Strvec {
concat_and(hundreds(num), tens_and_units(num))
}
fn concat_and(v1: Strvec, v2: Strvec) -> Strvec {
match (v1.len(), v2.len()) {
(_, 0) => v1,
(0, _) => v2,
(_, _) => [v1, vec!["and"], v2].concat(),
}
}
fn map(num: u64) -> &'static str {
match num {
0 => "zero",
1 => "one",
2 => "two",
3 => "three",
4 => "four",
5 => "five",
6 => "six",
7 => "seven",
8 => "eight",
9 => "nine",
10 => "ten",
11 => "eleven",
12 => "twelve",
13 => "thirteen",
14 => "fourteen",
15 => "fifteen",
16 => "sixteen",
17 => "seventeen",
18 => "eighteen",
19 => "nineteen",
20 => "twenty",
30 => "thirty",
40 => "fourty",
50 => "fifty",
60 => "sixty",
70 => "seventy",
80 => "eightty",
90 => "ninety",
100 => "hundred",
1_000 => "thousand",
1_000_000 => "million",
1_000_000_000 => "billion",
1_000_000_000_000 => "trillion",
1_000_000_000_000_000 => "quadrillion",
_ => "big number",
}
}