22: Improve solution for Rust track exercise "Beer Song".

[?]

Aaw9nJhsNmfzFih9mKyNw9mV8CgERXJkRa1kK1Kx3LQH

Aug 24, 2021, 6:20 PM

ZZLDUSP36F66GUAMMCV6DA2PBJFUNGUJKACYI5UWJKIXNDZZ4KSAC

Dependencies

[2] NQKFZ2HD 21: Improve solution for Rust track exercise "Beer Song" (remove unnecessary `f64` casts/conversions).
[3] 6DOVDD66 15: Add solution for Rust track exercise "Beer Song".
[4] 7NUHCTMK 16: Apply `cargo fmt` and `cargo clippy` to the solution for Rust track exercise "Beer Song". Also add previous versions.
[5] QK6XE5XF 13: Add Rust track exercises "Beer Song", "Proverb", "Difference Of Squares", "Sum Of Multiples", "Grains", "Prime Factors", "Armstrong Numbers" and "Reverse String".
[6] Z4YP3EEK 19: Improve performance of solution for Rust track exercise "Beer Song" at the cost of duplication.

Change contents

replacement in rust/beer-song/src/lib.rs at line 1

[3.37668]→[3.1537:1564](∅→∅)

use std::convert::TryInto;

[3.37668]

[3.1564]

use std::ops::Range;
replacement in rust/beer-song/src/lib.rs at line 15

[3.2117]→[2.0:31](∅→∅),[2.31]→[3.2156:2191](∅→∅),[3.2156]→[3.2156:2191](∅→∅)

fn digits(a: usize) -> usize {
((a as f64).log10() as usize) + 1

[3.2117]

[3.2191]

fn range_digits(base: usize, range: Range<usize>) -> usize {
let (mut result, mut power, mut current_digits) = (0, 1, 0);
while power <= range.start {
power *= base;
current_digits += 1;
}
result += (power - range.start) * current_digits;
while power <= range.end {
let last_power = power;
power *= base;
current_digits += 1;
result += (power - last_power) * current_digits;
}
result -= (power - range.end) * current_digits;
result
edit in rust/beer-song/src/lib.rs at line 32

[3.2257]→[2.32:228](∅→∅),[2.228]→[3.12075:12091](∅→∅),[3.3819]→[3.12075:12091](∅→∅),[3.12091]→[2.229:346](∅→∅),[2.346]→[3.12219:12223](∅→∅),[3.12219]→[3.12219:12223](∅→∅),[3.12223]→[2.347:466](∅→∅),[2.466]→[3.12368:12440](∅→∅),[3.12368]→[3.12368:12440](∅→∅),[3.4167]→[3.37741:37744](∅→∅),[3.12440]→[3.37741:37744](∅→∅),[3.37741]→[3.37741:37744](∅→∅)

// Present conversions and type casts could be problematic for certain inputs.
fn range_digits(start: usize, end: usize) -> usize {
let (start_digits, end_digits) = (digits(start), digits(end));
let (a, b) = (
10_usize.pow(start_digits.try_into().unwrap()) - 1,
10_usize.pow((end_digits - 1).try_into().unwrap()) as usize,
);
(digits(a + 1)..=digits(b - 1)).fold(0, |acc, elem| {
acc + 9 * elem * 10_usize.pow((elem - 1).try_into().unwrap())
}) + ((a - start + 1) * start_digits)
+ ((end - b + 1) * end_digits)
}
replacement in rust/beer-song/src/lib.rs at line 50

[3.12494]→[2.467:504](∅→∅),[2.504]→[3.12539:12697](∅→∅),[3.12539]→[3.12539:12697](∅→∅)

+ range_digits(3, s as usize)
+ match e {
0 => LENGTHS[0] + LENGTHS[1] + LENGTHS[2],
1 => LENGTHS[1] + LENGTHS[2],
2 => LENGTHS[2],
_ => 0,
}

[3.12494]

[3.12697]

+ range_digits(
10,
Range {
start: 3,
end: (s + 1) as usize,
},
) + match e {
0 => LENGTHS[0] + LENGTHS[1] + LENGTHS[2],
1 => LENGTHS[1] + LENGTHS[2],
2 => LENGTHS[2],
_ => 0,
}