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Convert a non-negative integer num to its English words representation.
Test Cases
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 <= 2<sup>31</sup> - 1
Solution
class Solution {
private static final String[] LESS_THAN_20 = {
"", "One", "Two", "Three", "Four", "Five", "Six", "Seven", "Eight", "Nine",
"Ten", "Eleven", "Twelve", "Thirteen", "Fourteen", "Fifteen",
"Sixteen", "Seventeen", "Eighteen", "Nineteen"
};
private static final String[] TENS = {
"", "Ten", "Twenty", "Thirty", "Forty", "Fifty", "Sixty", "Seventy", "Eighty", "Ninety"
};
private static final String[] THOUSANDS = {
"", "Thousand", "Million", "Billion"
};
public String numberToWords(int num) {
if (num == 0) return "Zero";
StringBuilder sb = new StringBuilder();
int i = 0;
while (num > 0) {
int chunk = num % 1000;
if (chunk != 0) {
StringBuilder part = new StringBuilder();
helper(chunk, part);
if (!THOUSANDS[i].isEmpty()) part.append(THOUSANDS[i]).append(" ");
sb.insert(0, part);
}
num /= 1000;
i++;
}
return sb.toString().trim();
}
private void helper(int num, StringBuilder sb) {
if (num == 0) return;
if (num < 20) {
sb.append(LESS_THAN_20[num]).append(" ");
} else if (num < 100) {
sb.append(TENS[num / 10]).append(" ");
helper(num % 10, sb);
} else {
sb.append(LESS_THAN_20[num / 100]).append(" Hundred ");
helper(num % 100, sb);
}
}
}