Commit ece0ac3

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2017 primality test performance improvement (#10)

* perf: skip even numbers in primality test -> 2 will always be a factor if even * perf: more efficient square root limit for the primality test

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Lines changed: 5 additions & 2 deletions

Original file line number	Diff line number	Diff line change
`@@ -51,7 +51,7 @@`
`51`	`51`	//! [`Day 18`]: crate::year2017::day18
`52`	`52`	`use crate::util::parse::*;`
`53`	`53`
`54`		`-/// We only need the vrey first number from the input.`
	`54`	`+/// We only need the very first number from the input.`
`55`	`55`	`pub fn parse(input: &str) -> u32 {`
`56`	`56`	`input.unsigned()`
`57`	`57`	`}`
`@@ -69,7 +69,10 @@ pub fn part2(input: &u32) -> usize {`
`69`	`69`	`/// Simple [prime number check](https://en.wikipedia.org/wiki/Primality_test)`
`70`	`70`	`/// of all factors from 2 to √n inclusive.`
`71`	`71`	`fn composite(n: u32) -> Option<u32> {`
`72`		`- for f in 2..=n.isqrt() {`
	`72`	`+ if n % 2 == 0 {`
	`73`	`+ return Some(n);`
	`74`	`+ };`
	`75`	`+ for f in (3..).step_by(2).take_while(\|m\| m * m <= n) {`
`73`	`76`	`if n % f == 0 {`
`74`	`77`	`return Some(n);`
`75`	`78`	`}`

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