projecteuler.net/058/main.rs

struct Step { 
    i: i8,
    j: i8
}

struct Steps {
    l: usize,
    i: usize,
    j: usize,
    k: usize,
    s: usize,
}

impl Steps {
    fn new(n: usize) -> Steps {
        return Steps {
            i: n / 2,
            j: n / 2,
            l: 1,
            k: 1,
            s: 0
        };
    }

    fn ads(&mut self, s: &Step) {
        if s.i < 0 { self.i -= 1; }
        if s.i > 0 { self.i += 1; }
        if s.j < 0 { self.j -= 1; }
        if s.j > 0 { self.j += 1; }
    }

    fn next(&mut self, n: u32) {
        //self.corner = false;
        let mut sts = Vec::new();
        sts.push(Step { i: 0, j: 1 });
        sts.push(Step { i: -1, j: 0 });
        sts.push(Step { i: 0, j: -1 });
        sts.push(Step { i: 1, j: 0 });

        if self.k > self.l {
            //self.corner = true;
            self.k = 1;
            self.s += 1;
            if self.s == sts.len() {
                self.s = 0;
                self.l += 1;
            }
            if self.s == 2 {
                self.l += 1;
            }
            println!("{}", n);
        }
        
        let st = &sts[self.s];
        self.k += 1;
        self.ads(st);
    }

}

fn main() {
    let mut st = Steps::new(7);
    for n in 1..20 {
        st.next(n);
    }
}