#![allow(unused_mut, non_snake_case,unused_imports)] use std::iter; use std::cmp::{max, min, Ordering}; use std::mem::{swap}; use std::collections::{HashMap,BTreeMap,HashSet,BTreeSet,BinaryHeap,VecDeque}; use std::iter::FromIterator; // 高速 EOF要 //macro_rules! input {(source = $s:expr, $($r:tt)*) => {let mut iter = $s.split_whitespace();input_inner!{iter, $($r)*}};($($r:tt)*) => {let mut 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_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_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, usize1) => {read_value!($iter, usize) - 1};($iter:expr, $t:ty) => {$iter.next().unwrap().parse::<$t>().expect("Parse error")};} // 低速 EOF不要 macro_rules! input {(source = $s:expr, $($r:tt)*) => {let mut iter = $s.split_whitespace();let mut next = || { iter.next().unwrap() };input_inner!{next, $($r)*}};($($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),* )) => {( $(read_value!($next, $t)),* )};($next:expr, [ $t:tt ; $len:expr ]) => {(0..$len).map(|_| read_value!($next, $t)).collect::>()};($next:expr, chars) => {read_value!($next, String).chars().collect::>()};($next:expr, usize1) => {read_value!($next, usize) - 1};($next:expr, $t:ty) => {$next().parse::<$t>().expect("Parse error")};} /* 問題文============================================================ ================================================================= 解説============================================================= ================================================================ */ /// Equivalent to std::lowerbound and std::upperbound in c++ pub trait BinarySearch { fn lower_bound(&self, &T) -> usize; fn upper_bound(&self, &T) -> usize; } impl BinarySearch for [T] { fn lower_bound(&self, x: &T) -> usize { let mut low = 0; let mut high = self.len(); while low != high { let mid = (low + high) / 2; match self[mid].cmp(x) { Ordering::Less => { low = mid + 1; } Ordering::Equal | Ordering::Greater => { high = mid; } } } low } fn upper_bound(&self, x: &T) -> usize { let mut low = 0; let mut high = self.len(); while low != high { let mid = (low + high) / 2; match self[mid].cmp(x) { Ordering::Less | Ordering::Equal => { low = mid + 1; } Ordering::Greater => { high = mid; } } } low } } fn main(){ input!(N:usize,X:usize,a:[usize;N]); let mut a:Vec = a; a.sort(); let mut ans = 0; for v in &a{ if *v > X{ break; } let aj = X - *v; let l = a.lower_bound(&aj); let r = a.upper_bound(&aj); ans += r-l; } println!("{}",ans); }