Top 3 Stacks Interview Questions
Browse 3 real-world technical and behavioral interview questions about Stacks. Review scenarios, edge cases, and architectural best practices.
Find the largest rectangle in a histogram in linear time, and tell me what the stack holds at every step.
Keep a stack of bar indices with strictly increasing heights. When a bar no taller than the top arrives, pop: the popped bar's rectangle runs from just after the new top to just before the current bar. A height-zero sentinel flushes the stack. Each index is pushed once and popped at most once, so it is O(n).
Implement a FIFO queue using only two stacks, then tell me what a dequeue costs.
Push arrivals onto an inbound stack and serve departures from an outbound one, transferring everything across only when the outbound stack is empty. Transferring on every dequeue instead reverses the order and breaks FIFO, and the empty-only rule is also what makes the amortised cost constant.
For each element of an array, find the first element to its right that is larger. State the invariant your stack maintains.
Scan left to right holding a stack of indices whose answers are still unknown, kept strictly decreasing by value. Each new element resolves and pops everything smaller than it, then pushes itself. Every index is pushed once and popped at most once, so the scan is O(n) despite the inner loop.