//! # Bundled libraries //! //! ## `input` (private) //! //! Expanded to `crate::input`. //! //! ## `partition_point` (private) //! //! Expanded to `crate::partition_point`. // verify-helper: PROBLEM https://yukicoder.me/problems/no/723 /*#[macro_use] extern crate input as _;*/ use partition_point::RangeBoundsExt as _; fn main() { input! { n: usize, x: u32, mut r#as: [u32; n], } r#as.sort(); let ans = (0..n) .map(|i| { let s = (i..n).partition_point(|j| r#as[i] + r#as[j] <= x); let t = (i..n).partition_point(|j| r#as[i] + r#as[j] < x); 2 * (s - t) - usize::from(2 * r#as[i] == x) }) .sum::(); println!("{}", ans); } // The following code was expanded by `cargo-equip`. #[allow(dead_code)] mod input { pub use crate::{input, input_inner, read, readable}; use std::{ cell::RefCell, fmt::Debug, io::{self, BufRead, Read}, rc::Rc, str::{FromStr, SplitWhitespace}, }; #[macro_export] macro_rules! input { (from $scanner:ident; $($tt:tt)*) => { $crate::input::input_inner!(@scanner($scanner), @tts($($tt)*)) }; ($($tt:tt)*) => { let __scanner = $crate::input::DEFAULT_SCANNER.with(|__scanner| __scanner.clone()); let mut __scanner_ref = __scanner.borrow_mut(); if let $crate::input::Scanner::Uninited = *__scanner_ref { *__scanner_ref = $crate::input::Scanner::stdin_auto().unwrap(); } $crate::input::input_inner!(@scanner(__scanner_ref), @tts($($tt)*)); ::std::mem::drop(__scanner_ref); ::std::mem::drop(__scanner); }; } #[macro_export] macro_rules! input_inner { (@scanner($scanner:ident), @tts()) => {}; (@scanner($scanner:ident), @tts(mut $single_tt_pat:tt : $readable:tt)) => { let mut $single_tt_pat = $crate::input::read!(from $scanner { $readable }); }; (@scanner($scanner:ident), @tts($single_tt_pat:tt : $readable:tt)) => { let $single_tt_pat = $crate::input::read!(from $scanner { $readable }); }; (@scanner($scanner:ident), @tts(mut $single_tt_pat:tt : $readable:tt, $($rest:tt)*)) => { $crate::input::input_inner!(@scanner($scanner), @tts(mut $single_tt_pat: $readable)); $crate::input::input_inner!(@scanner($scanner), @tts($($rest)*)); }; (@scanner($scanner:ident), @tts($single_tt_pat:tt : $readable:tt, $($rest:tt)*)) => { $crate::input::input_inner!(@scanner($scanner), @tts($single_tt_pat: $readable)); $crate::input::input_inner!(@scanner($scanner), @tts($($rest)*)); }; } #[macro_export] macro_rules! read { (from $scanner:ident { [$tt:tt] }) => { $crate::input::read!(from $scanner { [$tt; $crate::read!(from $scanner { usize })] }) }; (from $scanner:ident { [$tt:tt; $n:expr] }) => { (0..$n).map(|_| $crate::input::read!(from $scanner { $tt })).collect::>() }; (from $scanner:ident { ($($tt:tt),+) }) => { ($($crate::read!(from $scanner { $tt })),*) }; (from $scanner:ident { $ty:ty }) => { <$ty as $crate::input::Readable>::read_from_scanner(&mut $scanner) }; } #[macro_export] macro_rules! readable { ($name:ident; |$scanner:ident| { $($body:tt)* }) => { $crate::input::readable!($name; |$scanner| -> () { $($body)* }); }; ($name:ident; |$scanner:ident| $expr:expr) => { $crate::input::readable!($name; |$scanner| -> () { $expr }); }; ($name:ident; |$scanner:ident| -> $output:ty { $($body:tt)* }) => { enum $name {} impl $crate::input::Readable for $name { type Output = $output; fn read_from_scanner(mut $scanner: &mut $crate::input::Scanner) -> $output { $($body)* } } }; } pub enum Scanner { Uninited, Once { words: SplitWhitespace<'static>, }, Lines { rdr: Box, words: SplitWhitespace<'static>, }, } impl Scanner { pub fn stdin_auto() -> io::Result { if cfg!(debug_assertions) { Ok(Self::lines(Box::leak(Box::new(io::stdin())).lock())) } else { Self::once(io::stdin()) } } pub fn once(mut rdr: R) -> io::Result { let mut buf = String::with_capacity(1024); rdr.read_to_string(&mut buf)?; let words = Box::leak(buf.into_boxed_str()).split_whitespace(); Ok(Self::Once { words }) } pub fn lines(rdr: R) -> Self { Self::Lines { rdr: Box::new(rdr), words: "".split_whitespace(), } } pub fn parse_next_unwrap(&mut self) -> T where T::Err: Debug, { match self { Self::Uninited => None, Self::Once { words } => words.next(), Self::Lines { rdr, words } => words.next().or_else(|| { let mut line = "".to_owned(); rdr.read_line(&mut line).unwrap(); *words = Box::leak(line.into_boxed_str()).split_whitespace(); words.next() }), } .expect("reached EOF") .parse() .unwrap() } } thread_local! { pub static DEFAULT_SCANNER: Rc> = Rc::new(RefCell::new(Scanner::Uninited)); } pub trait Readable { type Output; fn read_from_scanner(scanner: &mut Scanner) -> Self::Output; } impl Readable for T where T::Err: Debug, { type Output = Self; fn read_from_scanner(scanner: &mut Scanner) -> Self { scanner.parse_next_unwrap() } } } #[allow(dead_code)] mod partition_point { use std::{ fmt, ops::{Add, Bound, Div, RangeBounds, Sub}, }; pub trait RangeBoundsExt: RangeBounds { fn partition_point

(&self, mut pred: P) -> T where P: FnMut(T) -> bool, { let mut start = match self.start_bound() { Bound::Included(&x) => x, Bound::Excluded(&x) if x > T::MIN_VALUE => x - T::ONE, _ => T::MIN_VALUE, }; let mut end = match self.end_bound() { Bound::Included(&x) if x < T::MAX_VALUE => x + T::ONE, Bound::Excluded(&x) => x, _ if pred(T::MAX_VALUE) => { panic!("the predicate is satisfied at {:?}", T::MAX_VALUE) } _ => T::MAX_VALUE, }; while start != end { let mid = start + (end - start) / (T::ONE + T::ONE); if pred(mid) { start = mid + T::ONE; } else { end = mid; } } start } } impl> RangeBoundsExt for R {} pub trait SliceExt { type Item; fn partition_point

(&self, pred: P) -> usize where P: FnMut(&Self::Item) -> bool; } impl SliceExt for [T] { type Item = T; fn partition_point

(&self, mut pred: P) -> usize where P: FnMut(&T) -> bool, { (0..self.len()).partition_point(|i| pred(&self[i])) } } pub trait PrimitiveInteger: Copy + Ord + Add + Sub + Div + fmt::Debug { const ZERO: Self; const ONE: Self; const MIN_VALUE: Self; const MAX_VALUE: Self; } macro_rules! impl_primitive_integer(($($ty:ty),*) => { $( impl PrimitiveInteger for $ty { const ZERO: Self = 0; const ONE: Self = 1; const MIN_VALUE: Self = <$ty>::min_value(); const MAX_VALUE: Self = <$ty>::max_value(); } )* }); impl_primitive_integer!(i8, i16, i32, i64, i128, isize, u8, u16, u32, u64, u128, usize); }