Stacks & Queues

Two humble rules, LIFO and FIFO, doing surprisingly heavy lifting.

1. 1Stack BasicsLast one in is the first one out.4m
2. 2Valid ParenthesesA closing bracket must answer the newest opening one.5m
3. 3Queue BasicsFirst one in is the first one out.4m
4. 4Queue From Two StacksReverse a reversal and LIFO turns into FIFO.5m
5. 5Monotonic StackKeep the stack ordered and every item waits only once.6m