Description
Convert a non-negative integer to its english words representation. Given input is guaranteed to be less than $2^{31} - 1$.
Example
Example 1:1
2Input: 123
Output: "One Hundred Twenty Three"
Example 2:1
2Input: 12345
Output: "Twelve Thousand Three Hundred Forty Five"
Example 3:
Input: 1234567
Output: “One Million Two Hundred Thirty Four Thousand Five Hundred Sixty Seven”1
**Example 4:**
Input: 1234567891
Output: “One Billion Two Hundred Thirty Four Million Five Hundred Sixty Seven Thousand Eight Hundred Ninety One”1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
## Solution
```java
class Solution {
private final String[] belowTen = new String[] {"", "One", "Two", "Three", "Four", "Five", "Six", "Seven", "Eight", "Nine"};
private final String[] belowTwenty = new String[] {"Ten", "Eleven", "Twelve", "Thirteen", "Fourteen", "Fifteen", "Sixteen", "Seventeen", "Eighteen", "Nineteen"};
private final String[] belowHundred = new String[] {"", "Ten", "Twenty", "Thirty", "Forty", "Fifty", "Sixty", "Seventy", "Eighty", "Ninety"};
public String numberToWords(int num) {
if (num == 0) return "Zero";
return helper(num);
}
private String helper(int num){
String res = "";
if (num < 10) res = belowTen[num];
else if (num < 20) res = belowTwenty[num-10];
else if (num < 100) res = belowHundred[num/10] + " " + helper(num%10);
else if (num < 1000) res = helper(num/100) +" Hundred " + helper(num%100);
else if (num < 1000000) res = helper(num/1000) + " Thousand " + helper(num%1000);
else if (num < 1000000000) res = helper(num/1000000) + " Million " + helper(num%1000000);
else res = helper(num/1000000000) + " Billion " + helper(num%1000000000);
return res.trim();
}
}