Simplify Path

Intuition

Splitting the path on the slash character breaks it into tokens where each token is either a directory name, a single period, a double period, or an empty string produced by consecutive slashes. A stack mirrors how a file system tracks the current directory chain: entering a named directory pushes it, and moving up with a double period pops the most recent one. The current-directory token and empty tokens carry no information, so we simply skip them. When popping on a double period we must guard against an empty stack, since going above the root just stays at the root. Rebuilding the answer is then a matter of prefixing each remaining stack entry with a slash.

Algorithm walkthrough

1. 1Split the input string on the slash character to obtain a list of raw tokens.
2. 2Iterate over the tokens, skipping any that are empty or equal to a single period.
3. 3When the token is a double period, pop the stack if it is non-empty so you move up one directory.
4. 4Otherwise treat the token as a real directory name and push it onto the stack.
5. 5After processing every token, join the stack entries with a slash separator.
6. 6Prefix the joined result with a leading slash so the root is always present, which also yields '/' when the stack is empty.

Implementation

class Solution:
    def simplifyPath(self, path: str) -> str:
        stack = []
        for token in path.split('/'):
            if token == '' or token == '.':
                continue
            if token == '..':
                if stack:
                    stack.pop()
            else:
                stack.append(token)
        return '/' + '/'.join(stack)