Convert a non-negative integer num to its English words representation.
Example 1
Input: num = 1234567
Output: One Million Two Hundred Thirty Four Thousand Five Hundred Sixty Seven
Explanation: Split the number into groups of three digits: 1 | 234 | 567. That reads "One Million", "Two Hundred Thirty Four Thousand" and "Five Hundred Sixty Seven".
Example 2
Input: num = 123
Output: One Hundred Twenty Three
Explanation: 123 is one hundred, twenty and three: "One Hundred Twenty Three".
Example 3
Input: num = 12345
Output: Twelve Thousand Three Hundred Forty Five
Explanation: 12345 splits into 12 | 345, which reads "Twelve Thousand" and "Three Hundred Forty Five".
Split the number into 3-digit groups from the right. Spell each group (hundreds/tens/ones) and append its scale word — Thousand, Million, Billion.
Run checks all cases above. Submit evaluates all test cases.