leetcode-problemset/leetcode-cn/problem (English)/删列造序 II(English) [delete-columns-to-make-sorted-ii].html

<p>You are given an array of <code>n</code> strings <code>strs</code>, all of the same length.</p>

<p>We may choose any deletion indices, and we delete all the characters in those indices for each string.</p>

<p>For example, if we have <code>strs = [&quot;abcdef&quot;,&quot;uvwxyz&quot;]</code> and deletion indices <code>{0, 2, 3}</code>, then the final array after deletions is <code>[&quot;bef&quot;, &quot;vyz&quot;]</code>.</p>

<p>Suppose we chose a set of deletion indices <code>answer</code> such that after deletions, the final array has its elements in <strong>lexicographic</strong> order (i.e., <code>strs[0] &lt;= strs[1] &lt;= strs[2] &lt;= ... &lt;= strs[n - 1]</code>). Return <em>the minimum possible value of</em> <code>answer.length</code>.</p>

<p>&nbsp;</p>
<p><strong>Example 1:</strong></p>

<pre>
<strong>Input:</strong> strs = [&quot;ca&quot;,&quot;bb&quot;,&quot;ac&quot;]
<strong>Output:</strong> 1
<strong>Explanation:</strong> 
After deleting the first column, strs = [&quot;a&quot;, &quot;b&quot;, &quot;c&quot;].
Now strs is in lexicographic order (ie. strs[0] &lt;= strs[1] &lt;= strs[2]).
We require at least 1 deletion since initially strs was not in lexicographic order, so the answer is 1.
</pre>

<p><strong>Example 2:</strong></p>

<pre>
<strong>Input:</strong> strs = [&quot;xc&quot;,&quot;yb&quot;,&quot;za&quot;]
<strong>Output:</strong> 0
<strong>Explanation:</strong> 
strs is already in lexicographic order, so we do not need to delete anything.
Note that the rows of strs are not necessarily in lexicographic order:
i.e., it is NOT necessarily true that (strs[0][0] &lt;= strs[0][1] &lt;= ...)
</pre>

<p><strong>Example 3:</strong></p>

<pre>
<strong>Input:</strong> strs = [&quot;zyx&quot;,&quot;wvu&quot;,&quot;tsr&quot;]
<strong>Output:</strong> 3
<strong>Explanation:</strong> We have to delete every column.
</pre>

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

<ul>
	<li><code>n == strs.length</code></li>
	<li><code>1 &lt;= n &lt;= 100</code></li>
	<li><code>1 &lt;= strs[i].length &lt;= 100</code></li>
	<li><code>strs[i]</code> consists of lowercase English letters.</li>
</ul>