Convert a non-negative integer to its english words representation. Given input is guaranteed to be less than 231 - 1.
For example
123 -> "One Hundred Twenty Three"
12345 -> "Twelve Thousand Three Hundred Forty Five"
1234567 -> "One Million Two Hundred Thirty Four Thousand Five Hundred Sixty Seven"
思路
- 题目首先告诉我们要3个一组的进行处理，而且限定了输入数字范围为0到231 - 1之间，最高只能到billion位，3个一组也只需处理四组即可，那么我们需要一个处理三个一组数字的函数。
- 需要把1到9，10 - 19的英文单词都列出来，分别放到2个数组里；还要把20,30，... 到90的英文单词列出来放到另一个数组里。
- 然后我们需要用技巧，比如一个三位数n
- 百位数表示为n/100
- 后两位数一起表示为n%100
- 十位数表示为n%100/10
- 个位数表示为n%10
- 然后我们看后两位数是否小于10 或者小于20，小于的话直接从数组中取出单词
- 如果大于等于20的话，则分别将十位和个位数字的单词从两个数组中取出来。
- 然后再来处理百位上的数字，还要记得加上Hundred。然后中间要插入"Thousand", "Million", "Billion"到对应的位置
- 最后check一下末尾是否有空格，把空格都删掉
Coner Case: 检查下输入是否为0 或者小于0，是的话要返回'Zero' 或者NULL。
class Solution {
String[] belowTen = {"","One","Two","Three","Four","Five","Six","Seven","Eight","Nine"};
String[] teens = {"Ten", "Eleven", "Twelve","Thirteen","Fourteen","Fifteen","Sixteen","Seventeen","Eighteen","Nineteen"};
String[] belowHundreds = {"","Ten","Twenty","Thirty","Forty","Fifty","Sixty","Seventy","Eighty","Ninety"};
public String numberToWords(int num) {
if (num < 0) return null;
if (num == 0) return "Zero";
return helper(num);
}
public String helper(int num) {
String result = new String();
if (num < 10) {
result = belowTen[num];
} else if (num < 20) {
result = teens[num % 10];
} else if (num < 100) {
result = belowHundreds[num / 10] + " " + belowTen[num % 10];
} else if (num < 1000) {
result = belowTen[num / 100] + " Hundred " + helper(num % 100);
} else if (num < 1000000) {
result = helper(num / 1000) + " Thousand " + helper(num % 1000);
} else if (num < 1000000000) {
result = helper(num / 1000000) + " Million " + helper(num % 1000000);
} else {
result = helper(num / 1000000000) + " Billion " + helper(num % 1000000000);
}
return result.trim();
}
}
