Stack/QueueStack & Queue

Stack (Bracket Matching)

A last-in, first-out collection where all insertions and removals happen at one end, the top.

Learn Stack →
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stack (bottom → top)
1/11Validate bracket nesting. A stack fits because the most recently opened bracket must be the first one closed — last in, first out.
Current characterOpener waiting on stackMatched pairMismatch
PseudocodeLearn Stack →
1stack = []
2for ch in s:
3  if ch is an opener: stack.push(ch)
4  else if stack empty or stack.top does not match ch: return invalid
5  else: stack.pop()
6return stack empty
Variables
i0
stackSize0
Complexity
access O(n)
search O(n)
insert O(1)
delete O(1)
Speed