アルゴリズムと数学 091

https://atcoder.jp/contests/math-and-algorithm/tasks/math_and_algorithm_br

しらみつぶしで十分速いです。

// How Many Ways?
#![allow(non_snake_case)]

use std::cmp::min;


//////////////////// library ////////////////////

fn read<T: std::str::FromStr>() -> T {
    let mut line = String::new();
    std::io::stdin().read_line(&mut line).ok();
    line.trim().parse().ok().unwrap()
}

fn read_vec<T: std::str::FromStr>() -> Vec<T> {
    read::<String>().split_whitespace()
            .map(|e| e.parse().ok().unwrap()).collect()
}


//////////////////// process ////////////////////

fn read_input() -> (i32, i32) {
    let v = read_vec();
    let N = v[0];
    let X = v[1];
    (N, X)
}

fn f(N: i32, X: i32) -> u32 {
    let mut counter = 0;
    let max_a = min(N, X/3-1);
    for a in 1..max_a+1 {
        let max_b = min(N, (X-a-1)/2);
        for b in a+1..max_b+1 {
            let c = X - a - b;
            if 1 <= c && c <= N {
                counter += 1
            }
        }
    }
    counter
}

fn main() {
    let (N, X) = read_input();
    println!("{}", f(N, X))
}