此题当中有很多要注意的点:
1. 各个字符数组的开头,都是空字符串;
2. less100的下标第1个字符串是空的;
3. 各个不同的空格;
4. 最后返回res得做trim()处理;
5. helper中的helper递归调用都是放在结尾的;
6. 还是背一背吧,哈哈
public class Solution {
private final String[] less20 = {"", "One", "Two", "Three", "Four", "Five", "Six", "Seven", "Eight", "Nine", "Ten", "Eleven", "Twelve", "Thirteen", "Fourteen", "Fifteen", "Sixteen", "Seventeen", "Eighteen", "Nineteen"};
private final String[] less100 = {"", "", "Twenty", "Thirty", "Forty", "Fifty", "Sixty", "Seventy", "Eighty", "Ninety"};
private final String[] more100 = {"", "Thousand", "Million", "Billion"};
public String numberToWords(int num) {
if (num == 0) {
return "Zero";
}
int i = 0;
String res = "";
while (num > 0) {
if (num % 1000 != 0) {
res = helper(num % 1000) + more100[i] + " " + res;
}
num = num / 1000;
i++;
}
return res.trim();
}
private String helper(int num) {
if (num == 0) {
return "";
} else if (num < 20) {
return less20[num] + " ";
} else if (num < 100) {
return less100[num/10] + " " + helper(num%10);
} else {
return less20[num/100] + " Hundred " + helper(num%100);
}
}
}