2020-1B Problem C

Wrong solution

fn case(i: usize, mut r: usize, s: usize) {
    let mut res: Vec<(usize, usize)> = Vec::new();

    while r >= 2 {
        let mut cs = s - 1;
        while cs > 0 {
            let a = r * (s - 1) - (s - 1 - cs);
            let b = r - 1;
            res.push((a, b));
            cs -= 1;
        }
        r -= 1;
    }

    println!("Case #{}: {}", i, res.len());
    for l in res {
        println!("{} {}", l.0, l.1);
    }
}

fn main() {
    let t: usize = read_ints()[0];
    for i in 0..t {
        let (r, s): (usize, usize) = {
            let l = read_ints();
            (l[0], l[1])
        };
        case(i + 1, r, s);
    }
}

// boilerplate omitted...