http://benchmarksgame.alioth.debian.org/u32/performance.php?test=regexdna

regexdna.rs

extern crate regexp;

static VARIANTS : [&'static str, ..9 ] = [
	"agggtaaa|tttaccct",
	"[cgt]gggtaaa|tttaccc[acg]",
	"a[act]ggtaaa|tttacc[agt]t",
	"ag[act]gtaaa|tttac[agt]ct",
	"agg[act]taaa|ttta[agt]cct",
	"aggg[acg]aaa|ttt[cgt]ccct",
	"agggt[cgt]aa|tt[acg]accct",
	"agggta[cgt]a|t[acg]taccct",
	"agggtaa[cgt]|[acg]ttaccct",
];

struct Subst<'a>(&'a str, &'a str);
static SUBST : [Subst<'static>, .. 11] = [
	Subst("B", "(c|g|t)"), Subst("D", "(a|g|t)"),   Subst("H", "(a|c|t)"), Subst("K", "(g|t)"),
	Subst("M", "(a|c)"),   Subst("N", "(a|c|g|t)"), Subst("R", "(a|g)"),   Subst("S", "(c|g)"),
	Subst("V", "(a|c|g)"), Subst("W", "(a|t)"),     Subst("Y", "(c|t)"),
];

fn replace(text: &str, regex: &str, rep: &str) -> ~str {
	regexp::Regexp::new(regex).unwrap().replace_all(text, regexp::NoExpand(rep))
}

fn count_matches(seq: &str, variant: &str) -> int {
	let mut n = 0;
	for _ in regexp::Regexp::new(variant).unwrap().captures_iter(seq) {
		n += 1;
	}
	return n
}

fn main() {
	let mut stdin =  std::io::stdio::stdin();
	let mut seq = stdin.read_to_str().unwrap();
	let ilen = seq.len();

	seq = replace(seq, ">[:^cntrl:]*[:cntrl:]*", "");
	seq = replace(seq, "[:cntrl:]+", "");
	let clen =  seq.len();


	for variant in VARIANTS.iter() {
		println!("{} {}", variant, count_matches(seq,*variant));
	}
	println!("");

	for &Subst(k, v) in SUBST.iter() {
		seq = replace(seq, k, v);
	}
	println!("{}", ilen);
	println!("{}", clen);
	println!("{}", seq.len());
}