minimum-deletions-to-make-string-balanced

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Algorithms

You are given a string <code>s</code> consisting only of characters <code>&#39;a&#39;</code> and <code>&#39;b&#39;</code>​​​​.

You can delete any number of characters in <code>s</code> to make <code>s</code> balanced. <code>s</code> is balanced if there is no pair of indices <code>(i,j)</code> such that <code>i &lt; j</code> and <code>s[i] = &#39;b&#39;</code> and <code>s[j]= &#39;a&#39;</code>.

Return the minimum number of deletions needed to make <code>s</code> balanced.

&nbsp;
Example 1:

<pre>
Input: s = &quot;aababbab&quot;
Output: 2
Explanation: You can either:
Delete the characters at 0-indexed positions 2 and 6 (&quot;aababbab&quot; -&gt; &quot;aaabbb&quot;), or
Delete the characters at 0-indexed positions 3 and 6 (&quot;aababbab&quot; -&gt; &quot;aabbbb&quot;).
</pre>

Example 2:

<pre>
Input: s = &quot;bbaaaaabb&quot;
Output: 2
Explanation: The only solution is to delete the first two characters.
</pre>

&nbsp;
Constraints:

<ul>
	<li><code>1 &lt;= s.length &lt;= 105</code></li>
	<li><code>s[i]</code> is&nbsp;<code>&#39;a&#39;</code> or <code>&#39;b&#39;</code>​​.</li>
</ul>

minimumDeletions

Minimum Deletions to Make String Balanced

Check if All A's Appears Before All B's

check-if-all-as-appears-before-all-bs

检查是否所有 A 都在 B 之前

Stack

String

Dynamic Programming

给你一个字符串&nbsp;<code>s</code>&nbsp;，它仅包含字符&nbsp;<code>'a'</code> 和&nbsp;<code>'b'</code>​​​​ 。

你可以删除&nbsp;<code>s</code>&nbsp;中任意数目的字符，使得&nbsp;<code>s</code> 平衡&nbsp;。当不存在下标对&nbsp;<code>(i,j)</code>&nbsp;满足&nbsp;<code>i &lt; j</code> ，且&nbsp;<code>s[i] = 'b'</code> 的同时&nbsp;<code>s[j]= 'a'</code> ，此时认为 <code>s</code> 是 平衡 的。

请你返回使 <code>s</code>&nbsp;平衡&nbsp;的 最少&nbsp;删除次数。

&nbsp;

示例 1：

<pre>
输入：s = "aababbab"
输出：2
解释：你可以选择以下任意一种方案：
下标从 0 开始，删除第 2 和第 6 个字符（"aababbab" -&gt; "aaabbb"），
下标从 0 开始，删除第 3 和第 6 个字符（"aababbab" -&gt; "aabbbb"）。
</pre>

示例 2：

<pre>
输入：s = "bbaaaaabb"
输出：2
解释：唯一的最优解是删除最前面两个字符。
</pre>

&nbsp;

提示：

<ul>
	<li><code>1 &lt;= s.length &lt;= 105</code></li>
	<li><code>s[i]</code>&nbsp;要么是&nbsp;<code>'a'</code> 要么是&nbsp;<code>'b'</code>​&nbsp;。​</li>
</ul>