Convert a non-negative integer num to its English words representation. 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"

class Solution {
    String[] numbers = {"Zero","One","Two","Three","Four","Five","Six","Seven","Eight","Nine","Ten","Eleven","Twelve","Thirteen","Fourteen","Fifteen","Sixteen","Seventeen","Eighteen","Nineteen"};
    String[] tens = {"","","Twenty","Thirty","Fourty","Fifty","Sixty","Seventy","Eighty","Ninety"};
    String[] thousands = {"","Thousand","Million","Billion"};
    
    public String numberToWords(int num) {
        if(num == 0) return "Zero";
        
        String res = "";
        int count = 0;
        while(num > 0 ){
            if(num % 1000 != 0){
                res = helper(num % 1000) + thousands[count] + " " + res;
            }
            num = num / 1000;
            count++;
        }
        return res.trim();
    }
    
    String helper(int num){
        if(num == 0) return "";
        if(