Simplify Path
mediumTime: O(n)Space: O(n)
Signals to notice
simplify Unix pathhandle . and .. and //stack for directory hierarchy
Brute force first
Not applicable — stack IS the natural approach.
The key insight
Split by '/'. For each part: '.' = skip, '..' = pop, '' = skip, else push. Join with '/' prefix. O(n).
What must stay true
The stack represents root-to-current path. '..' = go up (pop). Valid names = go deeper (push).
Easy way to go wrong
Popping empty stack on '..' — stay at root (don't pop).