// https://qiita.com/tanakh/items/0ba42c7ca36cd29d0ac8 macro_rules! input { ($($r:tt)*) => { let stdin = std::io::stdin(); let mut bytes = std::io::Read::bytes(std::io::BufReader::new(stdin.lock())); let mut next = move || -> String{ bytes.by_ref().map(|r|r.unwrap() as char) .skip_while(|c|c.is_whitespace()) .take_while(|c|!c.is_whitespace()) .collect() }; input_inner!{next, $($r)*} }; } macro_rules! input_inner { ($next:expr) => {}; ($next:expr,) => {}; ($next:expr, $var:ident : $t:tt $($r:tt)*) => { let $var = read_value!($next, $t); input_inner!{$next $($r)*} }; } macro_rules! read_value { ($next:expr, [ $t:tt ; $len:expr ]) => { (0..$len).map(|_| read_value!($next, $t)).collect::>() }; ($next:expr, usize1) => (read_value!($next, usize) - 1); ($next:expr, $t:ty) => ($next().parse::<$t>().expect("Parse error")); } fn inversion_by_merge(a: &mut [usize]) -> i64 { if a.len() <= 1 { return 0; } let mut ans = 0; let mut tmp = Vec::with_capacity(a.len()); { let mid = a.len() / 2; let (x, y) = a.split_at_mut(mid); ans += inversion_by_merge(x); ans += inversion_by_merge(y); let mut p0 = 0; let mut p1 = 0; while p0 < x.len() && p1 < y.len() { if x[p0] <= y[p1] { tmp.push(x[p0]); p0 += 1; } else { tmp.push(y[p1]); p1 += 1; ans += (x.len() - p0) as i64; } } while p0 < x.len() { tmp.push(x[p0]); p0 += 1; } while p1 < y.len() { tmp.push(y[p1]); p1 += 1; } } for i in 0..a.len() { a[i] = tmp[i]; } ans } fn main() { input! { n: usize, a: [usize1; n], b: [usize1; n], } let mut inva = vec![0; n]; for i in 0..n { inva[a[i]] = i; } let mut p = vec![0; n]; for i in 0..n { p[i] = inva[b[i]]; } println!("{}", inversion_by_merge(&mut p)); }