Convert a Number to Hexadecimal
<p>Given a 32-bit integer <code>num</code>, return <em>a string representing its hexadecimal representation</em>. For negative integers, <a href="https://en.wikipedia.org/wiki/Two%27s_complement" target="_blank">two&rsquo;s complement</a> method is used.</p>

<p>All the letters in the answer string should be lowercase characters, and there should not be any leading zeros in the answer except for the zero itself.</p>

<p><strong>Note:&nbsp;</strong>You are not allowed to use any built-in library method to directly solve this problem.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<pre><strong>Input:</strong> num = 26
<strong>Output:</strong> "1a"
</pre><p><strong class="example">Example 2:</strong></p>
<pre><strong>Input:</strong> num = -1
<strong>Output:</strong> "ffffffff"
</pre>
<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>-2<sup>31</sup> &lt;= num &lt;= 2<sup>31</sup> - 1</code></li>
</ul>
Bit Manipulation; Math; String
class Solution:
    def toHex(self, num: int) -> str:
        if num == 0:
            return '0'
        chars = '0123456789abcdef'
        s = []
        for i in range(7, -1, -1):
            x = (num >> (4 * i)) & 0xF
            if s or x != 0:
                s.append(chars[x])
        return ''.join(s)
