##### ###### ##### ### # # ### # # ###### ## ## ## ## ## ## ## # # # # # ## ##### #### ##### # # # # # # # #### ## # ## ## ## ## # # # # # ## ## # ###### ## ### # ### # ######
##### ###### ##### ### # # ### # # ###### ## ## ## ## ## ## ## # # # # # ## ##### #### ##### # # # # # # # #### ## # ## ## ## ## # # # # # ## ## # ###### ## ### # ### # ######
What you need first
Complete Stack Patterns first. Monotonic stacks maintain elements in sorted order (increasing or decreasing), which enables efficient "next greater/smaller element" queries.
The key pattern: when a new element violates the monotonic property, pop elements until the property is restored. Each element is pushed and popped at most once, giving total.
