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Algorithms

The Leetcode file system keeps a log each time some user performs a change folder operation.

The operations are described below:

<ul>
	<li><code>&quot;../&quot;</code> : Move to the parent folder of the current folder. (If you are already in the main folder, remain in the same folder).</li>
	<li><code>&quot;./&quot;</code> : Remain in the same folder.</li>
	<li><code>&quot;x/&quot;</code> : Move to the child folder named <code>x</code> (This folder is guaranteed to always exist).</li>
</ul>

You are given a list of strings <code>logs</code> where <code>logs[i]</code> is the operation performed by the user at the <code>ith</code> step.

The file system starts in the main folder, then the operations in <code>logs</code> are performed.

Return the minimum number of operations needed to go back to the main folder after the change folder operations.

&nbsp;
Example 1:

<img alt="" src="https://assets.leetcode.com/uploads/2020/09/09/sample_11_1957.png" style="width: 775px; height: 151px;" />

<pre>
Input: logs = [&quot;d1/&quot;,&quot;d2/&quot;,&quot;../&quot;,&quot;d21/&quot;,&quot;./&quot;]
Output: 2
Explanation: Use this change folder operation &quot;../&quot; 2 times and go back to the main folder.
</pre>

Example 2:

<img alt="" src="https://assets.leetcode.com/uploads/2020/09/09/sample_22_1957.png" style="width: 600px; height: 270px;" />

<pre>
Input: logs = [&quot;d1/&quot;,&quot;d2/&quot;,&quot;./&quot;,&quot;d3/&quot;,&quot;../&quot;,&quot;d31/&quot;]
Output: 3
</pre>

Example 3:

<pre>
Input: logs = [&quot;d1/&quot;,&quot;../&quot;,&quot;../&quot;,&quot;../&quot;]
Output: 0
</pre>

&nbsp;
Constraints:

<ul>
	<li><code>1 &lt;= logs.length &lt;= 103</code></li>
	<li><code>2 &lt;= logs[i].length &lt;= 10</code></li>
	<li><code>logs[i]</code> contains lowercase English letters, digits, <code>&#39;.&#39;</code>, and <code>&#39;/&#39;</code>.</li>
	<li><code>logs[i]</code> follows the format described in the statement.</li>
	<li>Folder names consist of lowercase English letters and digits.</li>
</ul>

minOperations

Crawler Log Folder

Baseball Game

baseball-game

棒球比赛

Backspace String Compare

backspace-string-compare

比较含退格的字符串

Stack

Array

String

每当用户执行变更文件夹操作时，LeetCode 文件系统都会保存一条日志记录。

下面给出对变更操作的说明：

<ul>
	<li><code>&quot;../&quot;</code> ：移动到当前文件夹的父文件夹。如果已经在主文件夹下，则 继续停留在当前文件夹 。</li>
	<li><code>&quot;./&quot;</code> ：继续停留在当前文件夹。</li>
	<li><code>&quot;x/&quot;</code> ：移动到名为 <code>x</code> 的子文件夹中。题目数据 保证总是存在文件夹 <code>x</code> 。</li>
</ul>

给你一个字符串列表 <code>logs</code> ，其中 <code>logs[i]</code> 是用户在 <code>ith</code> 步执行的操作。

文件系统启动时位于主文件夹，然后执行 <code>logs</code> 中的操作。

执行完所有变更文件夹操作后，请你找出 返回主文件夹所需的最小步数 。

&nbsp;

示例 1：

<img alt="" src="https://assets.leetcode-cn.com/aliyun-lc-upload/uploads/2020/09/26/sample_11_1957.png" style="height: 151px; width: 775px;">

<pre>输入：logs = [&quot;d1/&quot;,&quot;d2/&quot;,&quot;../&quot;,&quot;d21/&quot;,&quot;./&quot;]
输出：2
解释：执行 &quot;../&quot; 操作变更文件夹 2 次，即可回到主文件夹
</pre>

示例 2：

<img alt="" src="https://assets.leetcode-cn.com/aliyun-lc-upload/uploads/2020/09/26/sample_22_1957.png" style="height: 270px; width: 600px;">

<pre>输入：logs = [&quot;d1/&quot;,&quot;d2/&quot;,&quot;./&quot;,&quot;d3/&quot;,&quot;../&quot;,&quot;d31/&quot;]
输出：3
</pre>

示例 3：

<pre>输入：logs = [&quot;d1/&quot;,&quot;../&quot;,&quot;../&quot;,&quot;../&quot;]
输出：0
</pre>

&nbsp;

提示：

<ul>
	<li><code>1 &lt;= logs.length &lt;= 103</code></li>
	<li><code>2 &lt;= logs[i].length &lt;= 10</code></li>
	<li><code>logs[i]</code> 包含小写英文字母，数字，<code>&#39;.&#39;</code> 和 <code>&#39;/&#39;</code></li>
	<li><code>logs[i]</code> 符合语句中描述的格式</li>
	<li>文件夹名称由小写英文字母和数字组成</li>
</ul>