Simplify Path

Overview

Simplify path: given a Unix path string, return the canonical path. Rules: "/" is separator; "." = current dir (ignore); ".." = parent (pop segment); multiple slashes = one; trailing/leading slashes normalized. Use a stack of path segments: split by "/", drop empty and "."; for ".." pop if non-empty; else push. Result = "/" + stack.join("/").

When to Use

• Canonical path from user input or concatenated paths.
• Navigate / resolve relative segments (..) against a base.
• Stack for "undo" levels — same push/pop on "..".

How It Works

Split path by "/", keep only non-empty and not ".". Stack = current directory stack. ".." pops one level (if any); any other segment pushes. Root is always "/"; no ".." above root.

Example 1: Split + Stack (Standard)

function simplifyPath(path: string): string {
  const parts = path.split('/').filter(p => p !== '' && p !== '.');
  const stack: string[] = [];
  for (const p of parts) {
    if (p === '..') { if (stack.length > 0) stack.pop(); }
    else stack.push(p);
  }
  return '/' + stack.join('/');
}

Time: O(n). Space: O(n).

Example 2: Step-by-Step Trace

"/a/./b/../../c/". Parts: ["a","b","..","..","c"]. Push a → [a]. Push b → [a,b]. ".." pop → [a]. ".." pop → []. Push c → [c]. Result "/c".

"/../" → parts [".."] → pop on empty stack (no-op) → [] → "/".

Example 3: Edge Cases

• "/" — parts [] → stack [] → "/".
• "/home/" — ["home"] → "/home".
• "/../../" — ["..",".."] → pop, pop → "/".
• "a/b/../c" (relative) — typically problem says absolute; if relative, stack starts empty, result "a/c" (no leading "/").

Example 4: Single Pass Without Split

Scan character by character (or by slash); build current segment; on "/" or end, if segment is ".." pop stack, else if segment and not "." push. Handle leading slash and empty segment. Same logic, O(n) one pass.

Example 5: Return Segments or No Leading Slash

If the API needs an array of segments: return stack (no join). If canonical form has no leading "/" for relative paths, use stack.join("/") without prefix when path was relative.

Summary

• Simplify path: split by "/", drop "" and "."; stack: ".." pop else push; result "/" + join. See Stack Basics.