273. Integer to English Words
Hard
Convert a non-negative integer num to its English words representation.
Example 1:
Input: num = 123 Output: "One Hundred Twenty Three"
Example 2:
Input: num = 12345 Output: "Twelve Thousand Three Hundred Forty Five"
Example 3:
Input: num = 1234567 Output: "One Million Two Hundred Thirty Four Thousand Five Hundred Sixty Seven"
Constraints:
0 <= num <= 231 - 1
解法：
1.每000为一个 thousand level
2.单独函数处理每个000level -> helper(num)
如果是 0，return zero
如果是 1~19, 直接输出对应map
如果是 20～99， 输出 十位(20,30,...) + helper(xx % 10)
如果是 100～999， 输出 百位(one,two...) hundred + helper(xxx % 100)
class Solution { private String[] SMALLER_THAN_20 = {"", "One", "Two", "Three", "Four", "Five", "Six", "Seven", "Eight", "Nine", "Ten", "Eleven", "Twelve", "Thirteen", "Fourteen", "Fifteen", "Sixteen", "Seventeen", "Eighteen", "Nineteen"}; private String[] TENS = {"", "Ten", "Twenty", "Thirty", "Forty", "Fifty", "Sixty", "Seventy", "Eighty", "Ninety"}; private String[] THOUSANDS = {"", "Thousand", "Million", "Billion"}; public String numberToWords(int num) { //0直接返回 if(num == 0) return "Zero"; // String result = ""; //while loop resvole every 1000 for(int i = 0; num > 0; i++) { if(num % 1000 != 0) result = helper(num % 1000) + THOUSANDS[i] + " " +result; num /= 1000; } return result.trim(); } private String helper(int num) { if(num == 0) return ""; if(num < 20) { return SMALLER_THAN_20[num] + " "; } else if(num < 100) { return TENS[num / 10] + " " + helper(num % 10); } else{ return SMALLER_THAN_20[num / 100] + " Hundred " + helper(num % 100); } } }