Module c
Expand description
ยงABC 388 C - Various Kagamimochi
refs: https://atcoder.jp/contests/abc388/tasks/abc388_c
use proconio::input;
fn main() {
input! {
n: usize,
a: [usize; n],
}
let mut ans = 0;
for &ai in a.iter() {
let idx = binary_search(&a, ai * 2);
ans += n - idx - 1;
}
println!("{ans}");
}
fn binary_search(a: &[usize], x: usize) -> usize {
let mut l = 0;
let mut r = a.len();
while (r - l) > 1 {
let m = (l + r) / 2;
if a[m] < x {
l = m;
} else {
r = m;
}
}
l
}