leetcode-problemset/leetcode/problem/lexicographically-smallest-string-after-substring-operation.html

<p>You are given a string <code>s</code> consisting of only lowercase English letters. In one operation, you can do the following:</p>

<ul>
	<li>Select any non-empty substring of <code>s</code>, possibly the entire string, then replace each one of its characters with the previous character of the English alphabet. For example, &#39;b&#39; is converted to &#39;a&#39;, and &#39;a&#39; is converted to &#39;z&#39;.</li>
</ul>

<p>Return <em>the <strong>lexicographically smallest</strong> string you can obtain after performing the above operation <strong>exactly once</strong>.</em></p>

<p>A <strong>substring</strong> is a contiguous sequence of characters in a string.</p>
A string <code>x</code> is <strong>lexicographically smaller</strong> than a string <code>y</code> of the same length if <code>x[i]</code> comes before <code>y[i]</code> in alphabetic order for the first position <code>i</code> such that <code>x[i] != y[i]</code>.
<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> s = &quot;cbabc&quot;
<strong>Output:</strong> &quot;baabc&quot;
<strong>Explanation:</strong> We apply the operation on the substring starting at index 0, and ending at index 1 inclusive. 
It can be proven that the resulting string is the lexicographically smallest. 
</pre>

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

<pre>
<strong>Input:</strong> s = &quot;acbbc&quot;
<strong>Output:</strong> &quot;abaab&quot;
<strong>Explanation:</strong> We apply the operation on the substring starting at index 1, and ending at index 4 inclusive. 
It can be proven that the resulting string is the lexicographically smallest. 
</pre>

<p><strong class="example">Example 3:</strong></p>

<pre>
<strong>Input:</strong> s = &quot;leetcode&quot;
<strong>Output:</strong> &quot;kddsbncd&quot;
<strong>Explanation:</strong> We apply the operation on the entire string. 
It can be proven that the resulting string is the lexicographically smallest. 
</pre>

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

<ul>
	<li><code>1 &lt;= s.length &lt;= 3 * 10<sup>5</sup></code></li>
	<li><code>s</code> consists of lowercase English letters</li>
</ul>