MediumStacks

Simplify Path

Explanation & Solution

Description

Given an absolute path for a Unix-style file system, which begins with a slash '/', transform this path into its simplified canonical path.

In Unix-style file system context, a single period '.' signifies the current directory, a double period '..' denotes moving up one directory level, and multiple consecutive slashes such as '//' are interpreted as a single slash. In this problem, treat sequences of periods not covered by the previous rules (like '...') as valid names for files or directories.

The simplified canonical path should adhere to the following rules:

It must start with a single slash '/'.
Directories within the path must be separated by exactly one slash '/'.
It must not end with a slash '/', unless it's the root directory.
It must not include any single or double periods used to denote current or parent directories.

Input: path = "/home/"

Output: "/home"

Constraints

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

Approach

Stacks pattern

1. Split the Path

Split the path string by '/' to get individual components
This handles multiple consecutive slashes naturally (they become empty strings)

2. Process Each Component

Empty string or `'.'`: Skip — these don't change the directory
`'..'`: Pop from the stack (go up one directory), if stack is non-empty
Anything else: Push onto the stack as a valid directory name

3. Reconstruct the Path

Join the stack elements with '/' and prepend a leading '/'
If the stack is empty, the result is just '/' (root)

Key Insight

The stack naturally models directory navigation — pushing for descent, popping for ascent
Splitting by '/' and filtering edge cases makes the logic clean and linear
Time: O(n), Space: O(n)

Solution Code

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