Minimum Factorization
<p>Given a positive integer num, return <em>the smallest positive integer </em><code>x</code><em> whose multiplication of each digit equals </em><code>num</code>. If there is no answer or the answer is not fit in <strong>32-bit</strong> signed integer, return <code>0</code>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<pre><strong>Input:</strong> num = 48
<strong>Output:</strong> 68
</pre><p><strong class="example">Example 2:</strong></p>
<pre><strong>Input:</strong> num = 15
<strong>Output:</strong> 35
</pre>
<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= num &lt;= 2<sup>31</sup> - 1</code></li>
</ul>
Greedy; Math
func smallestFactorization(num int) int {
	if num < 2 {
		return num
	}
	ans, mul := 0, 1
	for i := 9; i >= 2; i-- {
		if num%i == 0 {
			for num%i == 0 {
				num /= i
				ans = mul*i + ans
				mul *= 10
			}
		}
	}
	if num < 2 && ans <= math.MaxInt32 {
		return ans
	}
	return 0
}