# 71. Simplify Path

You are given an *absolute* path for a Unix-style file system, which always begins with a slash `'/'`. Your task is to transform this absolute path into its **simplified canonical path**.

The *rules* of a Unix-style file system are as follows:

* A single period `'.'` represents the current directory.
* A double period `'..'` represents the previous/parent directory.
* Multiple consecutive slashes such as `'//'` and `'///'` are treated as a single slash `'/'`.
* Any sequence of periods that does **not match** the rules above should be treated as a **valid directory or** **file name**. For example, `'...'` and `'....'` are valid directory or file names.

The simplified canonical path should follow these *rules*:

* The path must start with a single slash `'/'`.
* Directories within the path must be separated by exactly one slash `'/'`.
* The path must not end with a slash `'/'`, unless it is the root directory.
* The path must not have any single or double periods (`'.'` and `'..'`) used to denote current or parent directories.

Return the **simplified canonical path**.

 

**Example 1:**

**Input:** path = "/home/"

**Output:** "/home"

**Explanation:**

The trailing slash should be removed.

**Example 2:**

**Input:** path = "/home//foo/"

**Output:** "/home/foo"

**Explanation:**

Multiple consecutive slashes are replaced by a single one.

**Example 3:**

**Input:** path = "/home/user/Documents/../Pictures"

**Output:** "/home/user/Pictures"

**Explanation:**

A double period `".."` refers to the directory up a level (the parent directory).

**Example 4:**

**Input:** path = "/../"

**Output:** "/"

**Explanation:**

Going one level up from the root directory is not possible.

**Example 5:**

**Input:** path = "/.../a/../b/c/../d/./"

**Output:** "/.../b/d"

**Explanation:**

`"..."` is a valid name for a directory in this problem.

 

**Constraints:**

* `1 <= path.length <= 3000`
* `path` consists of English letters, digits, period `'.'`, slash `'/'` or `'_'`.
* `path` is a valid absolute Unix path.

分析

注意split with '\\' 已经包含了'\\\\' '\\\\\\'的情况，后面 直接跳过空。

‘。。’和 stack not empty不能同时判断。

```
class Solution:
    def simplifyPath(self, path: str) -> str:

        ls = path.split('/')
        res = []
        for i in ls:
            if i == '.' or i == '':
                continue
            elif i == '..':
                if res:
                    res.pop()
            else:
                res.append(i)
 
        
        return '/' + ('/').join(res)
      


```