count-valid-prefixes

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Algorithms

You are given a binary string <code>s</code>.

A prefix of <code>s</code> is considered valid if its characters can be rearranged to form an alternating string.

Return the number of valid prefixes of <code>s</code>.

A string is considered alternating if no two adjacent characters are equal.

&nbsp;
Example 1:

<div class="example-block">
Input: s = &quot;00101&quot;

Output: 3

Explanation:

The valid prefixes are:

<ul>
	<li><code>&quot;0&quot;</code>: It is already an alternating string.</li>
	<li><code>&quot;001&quot;</code>: It can be rearranged into <code>&quot;010&quot;</code>, which is an alternating string.</li>
	<li><code>&quot;00101&quot;</code>: It can be rearranged into <code>&quot;01010&quot;</code>, which is an alternating string.</li>
</ul>

Thus, the answer is 3.
</div>

Example 2:

<div class="example-block">
Input: s = &quot;101&quot;

Output: 3

Explanation:

All prefixes of <code>s = &quot;101&quot;</code> are already alternating strings. Thus, the answer is 3.
</div>

&nbsp;
Constraints:

<ul>
	<li><code>1 &lt;= s.length &lt;= 100</code></li>
	<li><code>s</code> consists only of <code>&#39;0&#39;</code> and <code>&#39;1&#39;</code>.</li>
</ul>