Largest Rectangle in a Histogram — Solution & Editorial

Back to the Problem

Monotonic stack of (start, height): a bar lower than the stack top closes taller rectangles, and the popped rectangle's start extends the new bar's reach. Append a sentinel 0 to flush.

Complexity: O(N)

Watch out: Area reaches 10¹⁴ — 64-bit; and the popped bar's start index (not the current index) is where the merged bar begins.