Normalize a file path

Given an absolute Unix-style file path as a string, return its canonical normalized form.

Rules:

• The input always starts with /.
• A single . means the current directory and should be ignored.
• A double dot .. means move to the parent directory if possible.
• Multiple consecutive slashes should be treated as a single slash.
• The output must:
  • start with exactly one /
  • contain directory names separated by a single slash
  • not end with a trailing slash unless the result is the root path /

Example:

• Input: /a//b/./c/../d/
• Output: /a/b/d

Explain your approach and implement the function.

Normalize a Unix File Path

Constraints

• 1 <= path.length <= 3000
• path consists of English letters, digits, '.', '/', and '_'
• path is a valid absolute Unix path beginning with '/'

Hints

1. Split the path on '/' and process each component left to right with a stack.
2. Empty strings (from consecutive or trailing slashes) and '.' are no-ops; '..' pops the stack only if it is non-empty.
3. Tokens like '...' or '..foo' are ordinary directory names — only the exact strings '.' and '..' are special.
4. Rebuild the answer by joining the stack with '/' and prefixing a single '/'; an empty stack yields the root '/'.