https://atcoder.jp/contests/abc297/tasks/abc297_d
GCDを求めるのと同じですね。
// Count Subtractions #![allow(non_snake_case)] //////////////////// library //////////////////// fn read<T: std::str::FromStr>() -> T { let mut line = String::new(); std::io::stdin().read_line(&mut line).ok(); line.trim().parse().ok().unwrap() } fn read_vec<T: std::str::FromStr>() -> Vec<T> { read::<String>().split_whitespace() .map(|e| e.parse().ok().unwrap()).collect() } //////////////////// process //////////////////// fn read_input() -> (i64, i64) { let v = read_vec(); (v[0], v[1]) } fn f(A: i64, B: i64) -> i64 { if B == 0 { -1 } else { let q = A / B; let r = A % B; q + f(B, r) } } fn main() { let (A, B) = read_input(); println!("{}", f(A, B)) }