Find the next greater element for each item in an array using a monotonic stack.

The brute force is O(n squared) nested scans. A monotonic stack does it in one O(n) pass by keeping only the candidates that can still be a future answer. Here is the pattern and why each element is pushed and popped exactly once.

Updated Aug 2026 · Grounded in real Applied AI Engineer interview loops and written to a senior-engineer editorial bar.