Module c
Expand description
ยงABC 405 C - Sum of Product
refs: https://atcoder.jp/contests/abc405/tasks/abc405_c
use proconio::input;
fn main() {
input! {
n: usize,
a: [u64; n],
}
let sum_vec = a.iter().fold(vec![], |mut acc, &x| match acc.last() {
Some(&last) => {
acc.push(last + x);
acc
}
None => {
acc.push(x);
acc
}
});
let mut ans = 0;
for i in 1..n {
ans += sum_vec[i - 1] * a[i];
}
println!("{ans}");
}