Stacks & Queues

Problem	Complexity	Key Pattern
Daily Temperatures	O(n) -- each index pushed and popped at most once	Next-greater-element pattern — "next warmer day", "next higher price",
Min Stack	O(1) for all operations	Augmented data structure for O(1) aggregate queries — "get min/max
Valid Parentheses	O(n) -- single pass	Matching/nesting validation — balanced brackets, HTML tags, expression