fn run() { input! { n: usize, p: [usize; n], } let mut inv = vec![vec![0i32; n + 1]; n]; for j in 0..n { for i in (0..j).rev() { inv[i][j] = (p[i] > p[j]) as i32; inv[i][j] += inv[i + 1][j] + inv[i][j - 1] - inv[i + 1][j - 1]; } } let inf = 3000 * 3000; let mut dp = vec![-inf; n + 1]; dp[0] = 0; for _ in 0..n { let mut ndp = vec![-inf; n + 1]; for m in 1usize..n + 1 { let k = m.trailing_zeros(); let l = m - (1 << k); let r = (n + 1).min(m + (1 << k)); let val = |i: usize, j: usize| -> i32 { let s = m - 1 - j; let t = m + i; dp[s] + inv[s][t - 1] }; let pos = smawk(r - m, m - l, &|i, j, k| val(i, j) <= val(i, k)); for (i, (ndp, pos)) in ndp[m..].iter_mut().zip(pos).enumerate() { *ndp = std::cmp::max(*ndp, val(i, pos)); } } dp = ndp; println!("{}", inv[0][n - 1] - dp[n]); } } fn main() { run(); } // ---------- begin input macro ---------- // reference: https://qiita.com/tanakh/items/0ba42c7ca36cd29d0ac8 #[macro_export] macro_rules! input { (source = $s:expr, $($r:tt)*) => { let mut iter = $s.split_whitespace(); input_inner!{iter, $($r)*} }; ($($r:tt)*) => { let s = { use std::io::Read; let mut s = String::new(); std::io::stdin().read_to_string(&mut s).unwrap(); s }; let mut iter = s.split_whitespace(); input_inner!{iter, $($r)*} }; } #[macro_export] macro_rules! input_inner { ($iter:expr) => {}; ($iter:expr, ) => {}; ($iter:expr, $var:ident : $t:tt $($r:tt)*) => { let $var = read_value!($iter, $t); input_inner!{$iter $($r)*} }; } #[macro_export] macro_rules! read_value { ($iter:expr, ( $($t:tt),* )) => { ( $(read_value!($iter, $t)),* ) }; ($iter:expr, [ $t:tt ; $len:expr ]) => { (0..$len).map(|_| read_value!($iter, $t)).collect::>() }; ($iter:expr, chars) => { read_value!($iter, String).chars().collect::>() }; ($iter:expr, bytes) => { read_value!($iter, String).bytes().collect::>() }; ($iter:expr, usize1) => { read_value!($iter, usize) - 1 }; ($iter:expr, $t:ty) => { $iter.next().unwrap().parse::<$t>().expect("Parse error") }; } // ---------- end input macro ---------- fn smawk(row: usize, col: usize, select: &F) -> Vec where F: Fn(usize, usize, usize) -> bool, { let mut buf = vec![0; col + 2 * row]; let (col, mut buf) = buf.split_at_mut(col); for (i, c) in col.iter_mut().enumerate() { *c = i; } let mut stack: Vec<(usize, &[usize])> = vec![(row, col)]; loop { let &(h, col) = stack.last().unwrap(); if h == 1 { break; } let step = 1 << (stack.len() - 1); let mut po = 0; for &c in col.iter() { while po > 0 && select(step * (po - 1) + step - 1, buf[po - 1], c) { po -= 1; } if po < h { buf[po] = c; po += 1; } } let (ncol, tail) = buf.split_at_mut(po); buf = tail; stack.last_mut().unwrap().1 = ncol; stack.push((h / 2, ncol)); } let mut ans = vec![0; row]; while let Some((h, col)) = stack.pop() { for i in (0..(h / 2)).rev() { ans[2 * i + 1] = ans[i]; } let step = 1 << stack.len(); let mut j = 0; for (i, ans) in ans[..h].chunks_mut(2).enumerate() { let end = if ans.len() == 1 { *col.last().unwrap() } else { ans[1] }; let row = 2 * i * step + step - 1; let mut pos = col[j]; while col[j] != end { j += 1; if select(row, pos, col[j]) { pos = col[j]; } } ans[0] = pos; } } ans }