<p>Convert a non-negative integer <code>num</code> to its English words representation.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> num = 123
<strong>Output:</strong> &quot;One Hundred Twenty Three&quot;
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> num = 12345
<strong>Output:</strong> &quot;Twelve Thousand Three Hundred Forty Five&quot;
</pre>

<p><strong class="example">Example 3:</strong></p>

<pre>
<strong>Input:</strong> num = 1234567
<strong>Output:</strong> &quot;One Million Two Hundred Thirty Four Thousand Five Hundred Sixty Seven&quot;
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>0 &lt;= num &lt;= 2<sup>31</sup> - 1</code></li>
</ul>

singles = ["", "One", "Two", "Three", "Four", "Five", 
            "Six", "Seven", "Eight", "Nine"]
teens = ["Ten", "Eleven", "Twelve", "Thirteen", "Fourteen", 
        "Fifteen", "Sixteen", "Seventeen", "Eighteen", "Nineteen"]
tens = ["", "Ten", "Twenty", "Thirty", "Forty", "Fifty", 
        "Sixty", "Seventy", "Eighty", "Ninety"]
thousands = ["", "Thousand", "Million", "Billion"]

class Solution:
    def numberToWords(self, num: int) -> str:
        if num == 0:
            return "Zero"

        def toEnglish(num: int) -> str:
            s = ""
            if num >= 100:
                s += singles[num // 100] + " Hundred "
                num %= 100
            if num >= 20:
                s += tens[num // 10] + " "
                num %= 10
            if 0 < num < 10:
                s += singles[num] + " "
            elif num >= 10:
                s += teens[num - 10] + " "
            return s

        s = ""
        unit = int(1e9)
        for i in range(3, -1, -1):
            curNum = num // unit
            if curNum:
                num -= curNum * unit
                s += toEnglish(curNum) + thousands[i] + " "
            unit //= 1000
        return s.strip()
 
16700