P08 — Stacks and queues — every solution explained

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What is inside

• 1. Reverse a string using a stack
• 2. Balanced brackets across three kinds
• 3. Next strictly greater element to the right; -1 where there is none
• 4. Next strictly smaller element to the right; -1 where there is none
• 5. Previous strictly greater element to the left; -1 where there is none
• 6. Stock span: for each day, how many consecutive days back the price was <= today's
• 7. Evaluate a space-separated postfix expression over integers
• 8. Repeatedly remove adjacent duplicate characters until none remain
• 9. Do two strings match after applying '#' as a backspace?
• 10. Does the expression contain a redundant bracket pair, e.g. ((a+b)) or (a)?
• 11. Largest rectangle in a histogram, via a monotonic stack. O(n)
• 12. First non-repeating character in a stream, after each character arrives. '#' where every character seen so far repeats
• 13. A queue built from two stacks. Amortised O(1) per operation
• 14. A stack that also reports its minimum in O(1)