<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:
        vector<string> one = {"", "One", "Two", "Three", "Four", "Five", "Six", "Seven", "Eight", "Nine", "Ten", "Eleven", "Twelve", "Thirteen", "Fourteen", "Fifteen", "Sixteen", "Seventeen", "Eighteen", "Nineteen"};
    vector<string> zero = {"", "", "Twenty", "Thirty", "Forty", "Fifty", "Sixty", "Seventy", "Eighty", "Ninety"};
    vector<string> term = {"", "Thousand", "Million", "Billion"};
    string toEng(int num) {
        string ans = "";

        if (num >= 100) {
            auto result = div(num, 100);
            ans += one[result.quot] + " Hundred ";
            num = result.rem;
        }

        if (num >= 20) {
            auto result2 = div(num, 10);
            ans += zero[result2.quot];  // Fixed indexing for tens
            if (result2.rem > 0) {
                ans += " " + one[result2.rem];
            }
        } else if (num > 0) {
            ans += one[num];
        }

        if (!ans.empty() && ans.back() == ' ') {
            ans.pop_back();
        }

        return ans;
    }

    string numberToWords(int num) {
        if(num == 0){
            return "Zero";
        }

        string ans = "";
        int count = 0;
        while(num > 0){
            auto result = div(num, 1000);
            num = result.quot;
            if(result.rem > 0){
                string part = toEng(result.rem) + " " + term[count];
                ans = (ans.empty())? part : part + " " + ans;
            }
            count++;
        }

        if(!ans.empty() && ans.back() == ' ') ans.pop_back();

        return ans;
    }
};
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