整数的英语表示

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();}
}