Simplify Path
Difficulty: Medium
Category: DSA
Topics: String, Stack
Asked at: Facebook, Google, Amazon, Microsoft
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.