結果

問題 No.3469 ジャッジ結果の逆転数
コンテスト
ユーザー 👑 ArcAki
提出日時 2026-03-06 21:36:18
言語 Rust
(1.93.0 + proconio + num + itertools)
コンパイル:
/usr/bin/rustc_custom
実行:
./target/release/main
結果
AC  
実行時間 77 ms / 2,000 ms
コード長 7,488 bytes
記録
記録タグの例:
初AC ショートコード 純ショートコード 純主流ショートコード 最速実行時間
コンパイル時間 18,765 ms
コンパイル使用メモリ 225,344 KB
実行使用メモリ 12,228 KB
最終ジャッジ日時 2026-03-06 21:37:00
合計ジャッジ時間 3,039 ms
ジャッジサーバーID
（参考情報） 		judge6 / judge4
このコードへのチャレンジ
（要ログイン）
ファイルパターン 結果
sample AC * 3
other AC * 17
権限があれば一括ダウンロードができます

ソースコード

diff #
raw source code 

#[allow(unused_imports)]
use std::{
    convert::{Infallible, TryFrom, TryInto as _}, fmt::{self, Debug, Display, Formatter,},
    fs::File, hash::{Hash, Hasher, BuildHasherDefault}, iter::{Product, Sum}, marker::PhantomData,
    ops::{Add, AddAssign, Sub, SubAssign, Div, DivAssign, Mul, MulAssign, Neg, RangeBounds},
    str::FromStr, sync::{atomic::{self, AtomicU32, AtomicU64}, Once},
    collections::{*, btree_set::Range, btree_map::Range as BTreeRange}, mem::{swap},
    cmp::{self, Reverse, Ordering, Eq, PartialEq, PartialOrd},
    thread::LocalKey, f64::consts::PI, time::Instant, cell::RefCell,
    io::{self, stdin, Read, read_to_string, BufWriter, BufReader, stdout, Write},
};
pub mod fxhash {
    use std::hash::BuildHasherDefault;
    const K: u64 = 0x517c_c1b7_2722_0a95;
    #[derive(Default)]
    pub struct FxHasher {
        pub hash: u64,
    }
    impl FxHasher {
        #[inline(always)]
        fn mix_u64(mut h: u64, x: u64) -> u64 {
            h = h.rotate_left(5) ^ x;
            h = h.wrapping_mul(K);
            let x2 = x ^ (x >> 33) ^ (x << 11);
            h = h.rotate_left(5) ^ x2;
            h = h.wrapping_mul(K);
            h
        }

        #[inline(always)]
        fn write_u64_impl(&mut self, x: u64) {
            self.hash = Self::mix_u64(self.hash, x);
        }
    }

    impl std::hash::Hasher for FxHasher {
        #[inline(always)]
        fn finish(&self) -> u64 {
            self.hash
        }

        #[inline(always)]
        fn write(&mut self, bytes: &[u8]) {
            let mut h = self.hash;
            for &b in bytes {
                h = h.rotate_left(5) ^ (b as u64);
                h = h.wrapping_mul(K);
            }
            self.hash = h;
        }

        #[inline(always)]
        fn write_u64(&mut self, i: u64) { self.write_u64_impl(i); }
        #[inline(always)]
        fn write_u32(&mut self, i: u32) { self.write_u64_impl(i as u64); }
        #[inline(always)]
        fn write_u16(&mut self, i: u16) { self.write_u64_impl(i as u64); }
        #[inline(always)]
        fn write_u8 (&mut self, i: u8 ) { self.write_u64_impl(i as u64); }
        #[inline(always)]
        fn write_usize(&mut self, i: usize) { self.write_u64_impl(i as u64); }
        #[inline(always)]
        fn write_i64(&mut self, i: i64) { self.write_u64_impl(i as u64); }
        #[inline(always)]
        fn write_i32(&mut self, i: i32) { self.write_u64_impl(i as u64); }
        #[inline(always)]
        fn write_i16(&mut self, i: i16) { self.write_u64_impl(i as u64); }
        #[inline(always)]
        fn write_i8 (&mut self, i: i8 ) { self.write_u64_impl(i as u64); }
        #[inline(always)]
        fn write_isize(&mut self, i: isize) { self.write_u64_impl(i as u64); }
    }

    pub type FxBuildHasher = BuildHasherDefault<FxHasher>;
    pub type FxMap<K, V> = std::collections::HashMap<K, V, FxBuildHasher>;
    pub type FxSet<K> = std::collections::HashSet<K, FxBuildHasher>;
}

pub fn gcd(mut a: i64, mut b: i64)->i64{if a==0{return b;}else if b==0{return a;}let l1 = a.trailing_zeros();let l2 = b.trailing_zeros();
a >>= l1; b >>= l2;while a!=b{let x = (a^b).trailing_zeros();if a<b{swap(&mut a, &mut b)}a = (a-b)>>x;}a << l1.min(l2)}
pub fn factorial_i64(n: usize)->(Vec<i64>, Vec<i64>){ 
    let mut res = vec![1; n+1];let mut inv = vec![1; n+1];for i in 0..n{ res[i+1] = (res[i]*(i+1)as i64)%MOD; }
    inv[n] = mod_inverse(res[n], MOD);for i in (0..n).rev(){ inv[i] = inv[i+1]*(i+1) as i64%MOD; }(res, inv) }
pub fn floor(a:i64, b:i64)->i64{let res=(a%b+b)%b;(a-res)/b}
pub fn modulo(a: i64, b: i64)->i64{(a%b+b)%b}
pub fn extended_gcd(a:i64,b:i64)->(i64,i64,i64)
{if b==0{(a,1,0)}else{let(g,x,y)=extended_gcd(b,a%b);(g,y,x-floor(a,b)*y)}}
pub fn mod_inverse(a:i64,m:i64)->i64{let(_,x,_) =extended_gcd(a,m);(x%m+m)%m}
pub fn comb(a: i64, b: i64, f: &Vec<(i64, i64)>)->i64{
    if a<b{return 0;}else if b==0 || a==b{ return 1; }
    else{let x=f[a as usize].0;
        let y=f[(a-b) as usize].1;let z=f[b as usize].1;return((x*y)%MOD)*z%MOD;}}
pub fn factorial(x: i64)->Vec<(i64, i64)>{
    let mut f=vec![(1i64,1i64),(1, 1)];let mut z = 1i64;
    let mut inv = vec![0; x as usize+10];inv[1] = 1;
    for i in 2..x+1{z=(z*i)%MOD;
        let w=(MOD-inv[(MOD%i)as usize]*(MOD/i)%MOD)%MOD;
        inv[i as usize] = w;
        f.push((z, (f[i as usize-1].1*w)%MOD));}return f;}
pub fn fast_mod_pow(mut x: i64,p: usize, m: i64)->i64{
    x %= m;
    let mut res=1;let mut t=x;let mut z=p;while z > 0{
        if z%2==1{res = (res*t)%m;}t = (t*t)%m;z /= 2; }res}

pub trait SortD{ fn sort_d(&mut self); }
impl<T: Ord> SortD for Vec<T>{ fn sort_d(&mut self) {self.sort_by(|u, v| v.cmp(&u));} }
pub trait Mx{fn max(&self, rhs: Self)->Self;}
impl Mx for f64{ fn max(&self, rhs: Self)->Self{if *self < rhs{ rhs } else { *self } }}
pub trait Mi{ fn min(&self, rhs: Self)->Self; }
impl Mi for f64{ fn min(&self, rhs: Self)->Self{ if *self > rhs{ rhs } else { *self } } }
pub trait Chmax: PartialOrd + Copy {fn chmax(&mut self, rhs: Self) {if *self < rhs { *self = rhs; }}}
impl<T: PartialOrd + Copy> Chmax for T {}
pub trait Chmin: PartialOrd + Copy {fn chmin(&mut self, rhs: Self) {if *self > rhs { *self = rhs; }}}
impl<T: PartialOrd + Copy> Chmin for T {}
#[allow(unused)]
use proconio::{*, marker::*};
#[allow(unused)]
use fxhash::FxMap;

#[allow(dead_code)]
const INF: i64 = 1<<60;
#[allow(dead_code)]
const I: i32 = 1<<30;
#[allow(dead_code)]
const MOD: i64 = 998244353;
#[allow(dead_code)]
const D: [(usize, usize); 4] = [(1, 0), (0, 1), (!0, 0), (0, !0)];
#[allow(dead_code)]
pub fn c2d(c: u8)->(usize, usize){match c{b'U'=>(!0,0),b'D'=>(1,0),b'L'=>(0,!0),b'R'=>(0,1),_=>unreachable!()}}
#[allow(dead_code)]
pub fn c2d_i64(c: u8)->(i64, i64){match c{b'U'=>(-1,0),b'D'=>(1,0),b'L'=>(0,-1),b'R'=>(0,1),_=>unreachable!()}}
#[allow(dead_code)]
const D2: [(usize, usize); 8] = [(1, 0), (1, 1), (0, 1), (!0, 1), (!0, 0), (!0, !0), (0, !0), (1, !0)];

// [l, r)の半開区間で設定します。

pub struct BIT<T> where T: Copy + std::ops::Add<Output = T> + std::ops::Sub<Output = T> {
    n: usize,
    vec: Vec<T>,
    zero: T,
}

impl<T> BIT<T> where T: Copy + std::ops::Add<Output = T> + std::ops::Sub<Output = T> {
    pub fn new(n: usize, zero: T) -> Self {
        let k = n.next_power_of_two();
        let base = vec![zero; k + 2];
        BIT { n: k, vec: base, zero }
    }

    pub fn add(&mut self, mut idx: usize, x: T) {
        idx += 1;
        while idx <= self.n {
            self.vec[idx] = self.vec[idx] + x;
            idx += idx & (!idx + 1);
        }
    }

    pub fn g(&mut self, mut r: usize) -> T {
        let mut res = self.zero;
        while r > 0 {
            res = res + self.vec[r];
            r -= r & (!r + 1);
        }
        res
    }

    pub fn get(&mut self, l: usize, r: usize) -> T {
        self.g(r) - self.g(l)
    }
}

const MULTI: bool = false;
//#[fastout]
fn solve(){
    input!{
        n: usize, 
        a:[i32; n],
    }
    let mut b = a.clone();
    b.sort_unstable();b.dedup();
    let mut map = FxMap::default();
    for (i, &v) in b.iter().enumerate(){
        map.insert(v, i);
    }
    let mut ans = 0;
    let mut bit = BIT::new(n, 0i64);
    for &v in &a{
        let x = map[&v];
        ans += bit.get(x+1, n);
        bit.add(x, 1);
    }
    println!("{}", ans);
}

fn main() {
    if MULTI{
        input!{
            t: usize,
        }
        for _ in 0..t{
            solve();
        }
    } else {
        solve();
    }
}
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