Traversing the skill tree... found: potential
Traversing the skill tree... found: potential
LIFO and FIFO data structures for order-dependent problems
Given a string containing only the characters '(', ')', '{', '}', '[' and ']', determine if the input string has valid matching.
Given an array of integers, find the next greater element for each element.
Evaluate an arithmetic expression in Reverse Polish Notation (postfix notation).
Design a stack that supports push, pop, top, and retrieving the minimum element, all in O(1) time.
Given a binary tree, return its preorder traversal (root, left, right) using an iterative approach.
Given a string, repeatedly remove pairs of adjacent duplicate characters until no more removals are possible.
Master the fundamental pattern. Each problem teaches you when and how to apply this technique.