phone_letter.rs

#![allow(unused)]

extern crate itertools;
use itertools::Itertools;

fn phone_letter(number: &str) -> Vec<String> {
    number
        .chars()
        .filter_map(|digit| match digit {
            '2' => Some(vec!['a', 'b', 'c']),
            '3' => Some(vec!['d', 'e', 'f']),
            '4' => Some(vec!['g', 'h', 'i']),
            '5' => Some(vec!['j', 'k', 'l']),
            '6' => Some(vec!['m', 'n', 'o']),
            '7' => Some(vec!['p', 'q', 'r', 's']),
            '8' => Some(vec!['t', 'u', 'v']),
            '9' => Some(vec!['w', 'x', 'y', 'z']),
            _ => None,
        })
        .multi_cartesian_product()
        .map(|chars| chars.iter().collect::<String>())
        .collect()
}

#[test]
fn single_digit() {
    assert_eq!(phone_letter("9"), vec!["w", "x", "y", "z"]);
}

#[test]
fn multiple_digits() {
    assert_eq!(
        phone_letter("23"),
        vec!["ad", "ae", "af", "bd", "be", "bf", "cd", "ce", "cf"]
    );
}