<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>

class Solution {

public:

    // Arrays to store words for numbers less than 10, 20, and 100

    const vector<string> belowTen = { "", "One", "Two", "Three", "Four", "Five", "Six", "Seven", "Eight", "Nine" };

    const vector<string> belowTwenty = { "Ten", "Eleven", "Twelve", "Thirteen", "Fourteen", "Fifteen", "Sixteen", "Seventeen", "Eighteen", "Nineteen" };

    const vector<string> belowHundred = { "", "Ten", "Twenty", "Thirty", "Forty", "Fifty", "Sixty", "Seventy", "Eighty", "Ninety" };

    // Main function to convert a number to English words

    string numberToWords(int num) {

        // Handle the special case where the number is zero

        if (num == 0) {

            return "Zero";

        }

        // Call the helper function to start the conversion

        return convertToWords(num);

    }

private:

    // Recursive function to convert numbers to words

    // Handles numbers based on their ranges: <10, <20, <100, <1000, <1000000, <1000000000, and >=1000000000

    string convertToWords(int num) {

        if (num < 10) {

            return belowTen[num];

        }

        if (num < 20) {

            return belowTwenty[num - 10];

        }

        if (num < 100) {

            return belowHundred[num / 10] + (num % 10 ? " " + convertToWords(num % 10) : "");

        }

        if (num < 1000) {

            return convertToWords(num / 100) + " Hundred" + (num % 100 ? " " + convertToWords(num % 100) : "");

        }

        if (num < 1000000) {

            return convertToWords(num / 1000) + " Thousand" + (num % 1000 ? " " + convertToWords(num % 1000) : "");

        }

        if (num < 1000000000) {

            return convertToWords(num / 1000000) + " Million" + (num % 1000000 ? " " + convertToWords(num % 1000000) : "");

        }

        return convertToWords(num / 1000000000) + " Billion" + (num % 1000000000 ? " " + convertToWords(num % 1000000000) : "");

    }

};

    
        
    

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