「TRPL 3.5. 制御フロー」まとめの問題を解く

The Rust Programming Language

0. proconio

Cargo.toml

[dependencies]
proconio = "0.4.5"

1. 温度の変換

温度を華氏と摂氏で変換する。

$ ^\circ C = (^\circ F - 32) \times 5 \div 9 $

use proconio::input;

fn main() {
    input! {
        f: f64
    }
    println!("{}", to_c(f));
}

fn to_c(f: f64) -> f64 {
    (f - 32.0) * 5.0 / 9.0
}

$ ^\circ F = (^\circ C \times 9 \div 5) + 32 $

use proconio::input;

fn main() {
    input! {
        c: f64
    }
    println!("{}", to_f(c));
}

fn to_f(c: f64) -> f64 {
    (c * 9.0 / 5.0) + 32.0
}

2. フィボナッチ数列

フィボナッチ数列のn番目を生成する。

$ F_0 = 0, \ F_1 = 1, $
$ F_{n + 2} = F_n + F_{n + 1} \ (n \ge 0) $

use proconio::input;

fn main() {
    input! {
        n: u32  // 符号なし整数
    }
    println!("{}", fibonacci(n));
}

fn fibonacci(n: u32) -> u32 {
    if n < 2 {
        n
    } else {
        fibonacci(n - 2) + fibonacci(n - 1)
    }
}

3. The Twelve Days of Christmas

クリスマスキャロルの定番、"The Twelve Days of Christmas"の歌詞を、 曲の反復性を利用して出力する。

fn main() {
    // 序数と歌詞を用意
    const ORDINAL_NUMBERS: [&str; 12] = [
        "first", "second", "third", "fourth", "fifth", "sixth",
        "seventh", "eighth", "ninth", "tenth", "eleventh", "twelfth",
    ];
    const LYRICS: [&str; 12] = [
        "A partridge in a pear tree", "Two turtle doves, and",
        "Three french hens", "Four calling birds",
        "Five gold rings", "Six geese a-laying",
        "Seven swans a-swimming", "Eight maids a-milking",
        "Nine ladies dancing", "Ten lords a-leaping",
        "Eleven pipers piping", "Twelve drummers drumming",
    ];

    // i + 1 番の歌詞を出力
    for i in 0..12 {
        println!(
            "On the {} day of Christmas, my true love sent to me",
            ORDINAL_NUMBERS[i],
        );
        for j in (0..i + 1).rev() {
            println!("{}", LYRICS[j]);
        }
        println!();
    }
}