整数的英语表示

news2024/11/13 9:41:22

题目链接

整数的英语表示

题目描述

注意点

0 <= num <= 2^31 - 1

解答思路

每三个数字形成一组（高位不足的部分可以用0填充），使用StringBuilder拼接每组的数字和单位
关键是三个数字的英语表示，包含个位、十位、百位，找到三个数字值为0、[1, 9]、[10, 19]、[20, 99]、[100, 999]用英语表示的规律
可以先将[1, 9]、[10, 19]、[20, 99]以及单位存储到数组中，方便根据每一位的数字快速找到其英语表示，[100, 999]则是由单个数字 + “Hundred” + 十位/个位/无组成

代码

class Solution {
    String[] singles = {"", "One ", "Two ", "Three ", "Four ", "Five ", "Six ", "Seven ", "Eight ", "Nine "};
    String[] teens = {"Ten ", "Eleven ", "Twelve ", "Thirteen ", "Fourteen ", "Fifteen ", "Sixteen ", "Seventeen ", "Eighteen ", "Nineteen "};
    String[] tens = {"", "Ten ", "Twenty ", "Thirty ", "Forty ", "Fifty ", "Sixty ", "Seventy ", "Eighty ", "Ninety "};
    String[] thousands = {"", "Thousand ", "Million ", "Billion "};
    public String numberToWords(int num) {
        if (num == 0) {
            return "Zero";
        }
        StringBuilder res = new StringBuilder();
        String sNum = num + "";
        int remainder = sNum.length() % 3;
        String s = "";
        if (remainder == 1) {
            s = "00";
        }
        if (remainder == 2) {
            s = "0";
        }
        s = s + num;
        int n = s.length();
        int unit = n / 3 - 1;
        for (int i = 0; i < n; i += 3) {
            String tmp = buildWords(s, i);
            if (!"".equals(tmp)) {
                res.append(tmp);
                res.append(thousands[unit]);
            }
            unit--;
        }
        res.deleteCharAt(res.length() - 1);
        return res.toString();
    }

    public String buildWords(String s, int i) {
        StringBuilder sb = new StringBuilder();
        if (s.charAt(i) != '0') {
            sb.append(singles[s.charAt(i) - '0']);
            sb.append("Hundred").append(" ");
        }
        switch(s.charAt(i + 1)) {
            case '0':
                sb.append(singles[s.charAt(i + 2) - '0']);
                break;
            case '1':
                sb.append(teens[s.charAt(i + 2) - '0']);
                break;
            default:
                sb.append(tens[s.charAt(i + 1) - '0']);
                sb.append(singles[s.charAt(i + 2) - '0']);
                break;
        }
        return sb.toString();
    }
}