Integer to English Words LeetCode solution in Java

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class Solution {
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  private static final int[] INT_NUMBERS = {
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    1_000_000_000,
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    1_000_000,
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    1000,
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    100,
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    90,
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    80,
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    70,
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    60,
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    50,
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    40,
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    30,
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    20,
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    19,
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    18,
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    17,
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    16,
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    15,
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    14,
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    13,
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    12,
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    11,
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    10,
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    9,
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    8,
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    7,
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    6,
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    5,
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    4,
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    3,
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    2,
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    1
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  };
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  private static final String[] STRING_NUMBERS = {
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    "Billion",
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    "Million",
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    "Thousand",
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    "Hundred",
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    "Ninety",
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    "Eighty",
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    "Seventy",
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    "Sixty",
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    "Fifty",
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    "Forty",
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    "Thirty",
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    "Twenty",
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    "Nineteen",
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    "Eighteen",
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    "Seventeen",
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    "Sixteen",
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    "Fifteen",
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    "Fourteen",
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    "Thirteen",
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    "Twelve",
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    "Eleven",
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    "Ten",
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    "Nine",
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    "Eight",
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    "Seven",
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    "Six",
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    "Five",
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    "Four",
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    "Three",
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    "Two",
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    "One"
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  };
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  public String numberToWords(int num) {
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    if (num == 0) return "Zero";
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    return numberToWordsHelper(num).toString();
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  }
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  private StringBuilder numberToWordsHelper(int num) {
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    StringBuilder sb = new StringBuilder();
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    if (num == 0) return sb;
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    for (int i = 0; i < INT_NUMBERS.length; i++) {
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      if (num >= INT_NUMBERS[i]) {
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        if (num >= 100) {
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          sb.append(numberToWordsHelper(num / INT_NUMBERS[i]).append(" "));
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        }
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        sb.append(STRING_NUMBERS[i]).append(" ").append(numberToWordsHelper(num % INT_NUMBERS[i]));
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        break;
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      }
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    }
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    return sb.charAt(sb.length() - 1) == ' ' ? sb.deleteCharAt(sb.length() - 1) : sb; // trim
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  }
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}