Sequential Digits
<p>An&nbsp;integer has <em>sequential digits</em> if and only if each digit in the number is one more than the previous digit.</p>

<p>Return a <strong>sorted</strong> list of all the integers&nbsp;in the range <code>[low, high]</code>&nbsp;inclusive that have sequential digits.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<pre><strong>Input:</strong> low = 100, high = 300
<strong>Output:</strong> [123,234]
</pre><p><strong class="example">Example 2:</strong></p>
<pre><strong>Input:</strong> low = 1000, high = 13000
<strong>Output:</strong> [1234,2345,3456,4567,5678,6789,12345]
</pre>
<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>10 &lt;= low &lt;= high &lt;= 10^9</code></li>
</ul>
Enumeration
func sequentialDigits(low int, high int) (ans []int) {
	for i := 1; i < 9; i++ {
		x := i
		for j := i + 1; j < 10; j++ {
			x = x*10 + j
			if low <= x && x <= high {
				ans = append(ans, x)
			}
		}
	}
	sort.Ints(ans)
	return
}