#1193638 (Rust) No.1867 Partitions and Inversions

• 問題: No.1867 Partitions and Inversions
• ユーザー: akakimidori
• 提出日時: 2026-10-18 19:51:45
• 言語: Rust (1.99.0 + proconio + num + itertools + ACL)
• 結果: AC
• 実行時間: 1,709 ms / 5,000 ms
• コード長: 4,208 bytes
• コンパイル時間: 3,230 ms
• コンパイル使用メモリ: 191,556 KB
• 実行使用メモリ: 37,504 KB
• 最終ジャッジ日時: 2026-10-24 23:48:45
• 合計ジャッジ時間: 77,171 ms
• ジャッジサーバーID （参考情報）: judge5_0 / judge7_0

ファイルパターン	結果
sample	AC * 3
other	AC * 66

ソースコード

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, $t)).collect::<Vec<_>>()
    };
    ($iter:expr, chars) => {
        read_value!($iter, String).chars().collect::<Vec<char>>()
    };
    ($iter:expr, bytes) => {
        read_value!($iter, String).bytes().collect::<Vec<u8>>()
    };
    ($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<F>(row: usize, col: usize, select: &F) -> Vec<usize>
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
}