Monotonic-Stack

Parsing nested structures, simulations that interact with the previous element, monotonic stacks, greedy deletion for the smallest string, and a lazy-deletion Max Stack

LeetCode 4045 note: merge robots already close at t = 0, then go right to left like car fleets, where anything faster than the fleet ahead eventually joins it

LeetCode 1944 note: a decreasing monotonic stack from right to left; everyone popped is visible, and so is the person left on top

LeetCode 2355 note: ending at i, each shelf to the left takes one fewer book until a bottleneck shelf j with too few books; a monotonic stack finds j, and dp[i] = dp[j] + an arithmetic series

LeetCode 316 note: a monotonic stack with last positions; pop a larger top that appears again later, and skip letters already on the stack

LeetCode 1526 note: scanning left to right, every rise above the previous height needs that many new operations; drops reuse earlier operations

LeetCode 581 note: scanning left to right with a running max, the last index below it is the right boundary; scanning right to left with a running min, the last index above it is the left boundary

LeetCode 3555 note: every length-k window is one instance of LeetCode 581; with n only 1000, two O(k) scans per window are enough

LeetCode 1793 note: expand from k toward the larger neighbor each step so the minimum stays as large as possible for each length; at a boundary, only the other side can grow

LeetCode 1574 note: what remains is a non-decreasing prefix plus a non-decreasing suffix; find the longest of each, then join them with two pointers

LeetCode 3816 note: a monotonic stack that deletes a larger top while another copy exists, then trims duplicate letters off the end since a prefix is always smaller

Solving the Online Stock Span problem using monotonic stack approach