minimum-operations-to-sort-a-string

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Algorithms

You are given a string <code>s</code> consisting of lowercase English letters.

In one operation, you can select any substring of <code>s</code> that is not the entire string and sort it in non-descending alphabetical order.

Return the minimum number of operations required to make <code>s</code> sorted in non-descending order. If it is not possible, return -1.

&nbsp;
Example 1:

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

Output: 1

Explanation:​​​​​​​

<ul>
	<li>Sort substring <code>&quot;og&quot;</code> to <code>&quot;go&quot;</code>.</li>
	<li>Now, <code>s = &quot;dgo&quot;</code>, which is sorted in ascending order. Thus, the answer is 1.</li>
</ul>
</div>

Example 2:

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

Output: 2

Explanation:

<ul>
	<li>Sort substring <code>&quot;car&quot;</code> to <code>&quot;acr&quot;</code>, so <code>s = &quot;acrd&quot;</code>.</li>
	<li>Sort substring <code>&quot;rd&quot;</code> to <code>&quot;dr&quot;</code>, making <code>s = &quot;acdr&quot;</code>, which is sorted in ascending order. Thus, the answer is 2.</li>
</ul>
</div>

Example 3:

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

Output: -1

Explanation:

<ul>
	<li>It is impossible to sort <code>s</code> under the given constraints. Thus, the answer is -1.</li>
</ul>
</div>

&nbsp;
Constraints:

<ul>
	<li><code>1 &lt;= s.length &lt;= 105</code></li>
	<li><code>s</code> consists of only lowercase English letters.</li>
</ul>