Decrypt String from Alphabet to Integer Mapping
<p>You are given a string <code>s</code> formed by digits and <code>&#39;#&#39;</code>. We want to map <code>s</code> to English lowercase characters as follows:</p>

<ul>
	<li>Characters (<code>&#39;a&#39;</code> to <code>&#39;i&#39;</code>) are represented by (<code>&#39;1&#39;</code> to <code>&#39;9&#39;</code>) respectively.</li>
	<li>Characters (<code>&#39;j&#39;</code> to <code>&#39;z&#39;</code>) are represented by (<code>&#39;10#&#39;</code> to <code>&#39;26#&#39;</code>) respectively.</li>
</ul>

<p>Return <em>the string formed after mapping</em>.</p>

<p>The test cases are generated so that a unique mapping will always exist.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> s = &quot;10#11#12&quot;
<strong>Output:</strong> &quot;jkab&quot;
<strong>Explanation:</strong> &quot;j&quot; -&gt; &quot;10#&quot; , &quot;k&quot; -&gt; &quot;11#&quot; , &quot;a&quot; -&gt; &quot;1&quot; , &quot;b&quot; -&gt; &quot;2&quot;.
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> s = &quot;1326#&quot;
<strong>Output:</strong> &quot;acz&quot;
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= s.length &lt;= 1000</code></li>
	<li><code>s</code> consists of digits and the <code>&#39;#&#39;</code> letter.</li>
	<li><code>s</code> will be a valid string such that mapping is always possible.</li>
</ul>
String
func freqAlphabets(s string) string {
	var ans []byte
	for i, n := 0, len(s); i < n; {
		if i+2 < n && s[i+2] == '#' {
			num := (int(s[i])-'0')*10 + int(s[i+1]) - '0'
			ans = append(ans, byte(num+int('a')-1))
			i += 3
		} else {
			num := int(s[i]) - '0'
			ans = append(ans, byte(num+int('a')-1))
			i += 1
		}
	}
	return string(ans)
}
