Check if every opening bracket has a matching closing bracket in the correct order.
Build a first-in-first-out queue using only two last-in-first-out stacks.
Build a stack that also tells you the current minimum element in O(1) time.
Calculate the result of a math expression written in postfix notation like '2 1 + 3 *'.
For each number in an array, find the first larger number to its right.
Check if a string of parentheses is properly opened and closed.
Reverse a string by pushing all characters onto a stack and popping them off.
Evaluate a math expression written in postfix notation using a stack.
For each day, find how many days you have to wait until a warmer day comes.