projecteuler.net/032/main.rs

use std::collections::HashSet;

type Str = Vec<u8>;
type Res = HashSet<u32>;

fn pr(s: &Str) {
    for c in s.iter() { print!("{}", c); }
    println!("");
}

fn get_eq(s: &Str, p: usize, q: usize) -> (u32, u32, u32) {
    let mut a: u32 = 0;
    for i in 0..p {
        a *= 10;
        a += s[i] as u32;
    }
    let mut b: u32 = 0; 
    for i in p..q {
        b *= 10;
        b += s[i] as u32;
    }
    let mut c: u32 = 0;
    for i in q..s.len() {
        c *= 10;
        c += s[i] as u32;
    }
    return (a, b, c);
}

fn test(s: &Str, hs: &mut Res) {
    for p in 1..s.len() {
        for q in p..s.len() {
            let (a, b, c) = get_eq(&s, p, q);
            
            //println!("{} * {} = {}", a, b, c);
            
            if a * b == c {
                hs.insert(c);
                println!("{} * {} = {}", a, b, c);
            }
        }
    }
}

fn sp(s: &Str, fx: usize, k: usize) -> Str {
    let mut res = Vec::new();
    for i in 0..fx {
        res.push(s[i]);
    }
    res.push(s[k]);
    for i in fx..s.len() {
        if i != k { res.push(s[i]); }
    }
    res
}

fn lp(s: &Str, fx: usize, keep_first: bool, mut count: usize, hs: &mut Res) -> usize {
    let kf = 0; //if keep_first { 0usize } else { 1usize };
    for k in (fx + kf)..s.len() {
        let ss = sp(&s, fx, k);
        //count += 1;
        if  ss != *s || keep_first {
            count += 1;
            test(&ss, hs);
        }

        count = lp(&ss, fx + 1, false, count, hs);
    }
    count
}

fn main() {
    let mut s = Vec::new();
    s.push(1);
    s.push(2);
    s.push(3);
    s.push(4);
    s.push(5);
    s.push(6);
    s.push(7);
    s.push(8);
    s.push(9);
    
    //test(&s);
    let mut hs = HashSet::new();
    lp(&s, 0, true, 0, &mut hs);
    println!("count: {}", hs.len());
    let mut sum = 0u32;
    for p in hs {
        sum += p;
    }
    println!("sum = {}", sum);
}