【Rust】カレンダーを作る【Algorithm】

fn leap_year(year: u32) -> bool {
    if year % 4 == 0 && year % 100 != 0 || year % 400 == 0 {
        return true;
    } 
    false
}

fn day_of_week(year: usize, month: usize) -> usize {
    let mut days_of_month = [0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31];

    if leap_year(year.try_into().unwrap()) {
        days_of_month[2] = 29;
    }

    let day = 1;
    let mut days = 0;

    for y in 1..year {
        if leap_year(y.try_into().unwrap()) {
            days += 366
        } else {
            days += 365
        }
    }

    for m in 1..month {
        days += days_of_month[m as usize]
    }

    days += day;
    return days % 7
}

fn main() {
    let days_of_week_name = ["日".to_string(), "月".to_string(),"火".to_string(),"水".to_string(),"木".to_string(),"金".to_string(),"土".to_string()];

    let mut days_of_month = [0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31];
    let year = 2040;
    let month = 3;

    if leap_year(year.try_into().unwrap()) {
        days_of_month[2] = 29;
    }
    let first_day = day_of_week(year, month);

    println!("{}年 {}月", year, month);
    println!("日 月 火 水 木 金 土");
    let emp = " ".to_string();

    print!("{}", emp.repeat(first_day*3));
    for day in 1..(1 + days_of_month[month]) {
        print!("{:<2} ", day);
        if(day + first_day - 1) % 7 == 6 {
            print!("\n");
        }
    }
    print!("\n");
}

Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.14s
Running `target/debug/basic`
2040年 3月
日 月 火 水 木 金 土
1 2 3
4 5 6 7 8 9 10
11 12 13 14 15 16 17
18 19 20 21 22 23 24
25 26 27 28 29 30 31

これは中々面白い！！！　そんなに難しくないけど、中々思いつかない!