Module 4Reading Input (stdin)Lesson 6 of 2316 min

Real stdin API (copy-paste for local)

io::stdin, BufRead, fast-ish patterns you will use in contests.

Minimal local template

rust

// Local version (real stdin). On this site, use the simulated version in the exercise.
use std::io::{self, Read};

fn main() {
    let mut s = String::new();
    io::stdin().read_to_string(&mut s).unwrap();
    let mut it = s.split_whitespace();
    let n: usize = it.next().unwrap().parse().unwrap();
    let mut xs = Vec::with_capacity(n);
    for _ in 0..n {
        xs.push(it.next().unwrap().parse::<i32>().unwrap());
    }
    println!("{n} {:?}", xs);
}

Output

3 [10, 20, 30]

Why read_to_string + split_whitespace?

Simple and fine for most interview sizes. Contests sometimes use bulk reads for speed.

On this website

Run the simulated version below (string input). Locally, swap in real stdin.

Macro-style next token helper

rust

fn next<T: std::str::FromStr>(it: &mut impl Iterator<Item = &str>) -> T {
    it.next().unwrap().parse().ok().unwrap()
}

Challenge

Write next::<T> generic helper using FromStr and parse two f64s.

Tips

read_to_string for whole input
split_whitespace tokenizes all
Same logic for local contests

Try it live

Real stdin API (copy-paste for local)Rust 2021

Loading editor…

Output

Press Run to compile and execute.