fn number_to_letters(n: u32) -> String {
    if n == 0 {
        return "zero".to_string();
    }

    let ones = [
        "", "one", "two", "three", "four", "five", "six", "seven", "eight", "nine",
    ];
    let teens = [
        "ten",
        "eleven",
        "twelve",
        "thirteen",
        "fourteen",
        "fifteen",
        "sixteen",
        "seventeen",
        "eighteen",
        "nineteen",
    ];
    let tens = [
        "", "", "twenty", "thirty", "forty", "fifty", "sixty", "seventy", "eighty", "ninety",
    ];

    let mut result = String::new();
    let mut num = n;

    // 处理千位
    if num >= 1000 {
        let thousands = num / 1000;
        result.push_str(&number_to_letters_under_1000(
            thousands, &ones, &teens, &tens,
        ));
        result.push_str("thousand");
        num %= 1000;
        if num > 0 {
            result.push_str("and");
        }
    }

    // 处理百位以下
    if num > 0 {
        result.push_str(&number_to_letters_under_1000(num, &ones, &teens, &tens));
    }

    result
}

fn number_to_letters_under_1000(n: u32, ones: &[&str], teens: &[&str], tens: &[&str]) -> String {
    let mut result = String::new();
    let mut num = n;

    // 处理百位
    if num >= 100 {
        let hundreds = num / 100;
        result.push_str(ones[hundreds as usize]);
        result.push_str("hundred");
        num %= 100;
        if num > 0 {
            result.push_str("and");
        }
    }

    // 处理十位和个位
    if num >= 20 {
        let ten_digit = num / 10;
        result.push_str(tens[ten_digit as usize]);
        num %= 10;
        if num > 0 {
            result.push_str(ones[num as usize]);
        }
    } else if num >= 10 {
        result.push_str(teens[(num - 10) as usize]);
    } else if num > 0 {
        result.push_str(ones[num as usize]);
    }

    result
}

fn count_letters(text: &str) -> usize {
    text.chars().filter(|c| c.is_alphabetic()).count()
}

fn solve_letter_count(start: u32, end: u32) -> usize {
    (start..=end)
        .map(|n| count_letters(&number_to_letters(n)))
        .sum()
}

fn main() {
    // 验证 1-5 的例子
    let test_words = ["one", "two", "three", "four", "five"];
    let test_count: usize = test_words.iter().map(|w| w.len()).sum();
    println!("1到5的字母数: {test_count}");

    // 验证我们的函数
    let our_count = solve_letter_count(1, 5);
    println!("我们函数计算的1到5: {our_count}");

    // 计算 1 到 1000
    let result = solve_letter_count(1, 1000);
    println!("1到1000的字母总数: {result}");
}