Binary Tree Inorder Traversal
Traverse a binary tree in inorder (left -> root -> right)
Binary Tree Preorder Traversal
Traverse a binary tree in preorder (root -> left -> right)
Flatten Multilevel Linked List
Flatten a multilevel doubly linked list into a single level
Implement Queue using Stacks
Implement a queue using two stacks with O(1) amortized time complexity for all operations.
Implement Stack
Design and implement a stack data structure with push, pop, top, and empty operations
Implement Stack using Queues
Implement a stack using two queues with O(1) amortized time complexity for all operations.
Largest Rectangle in Histogram
Find the largest rectangle that can be formed in a histogram
Max Stack
Design a stack that supports push, pop, top, peekMax, and popMax operations
Min Stack
Design a stack that supports push, pop, top, and retrieving the minimum element in constant time
Minimum Insertions to Balance Parentheses
Find minimum insertions needed to balance parentheses string
Next Greater Element
Find the next greater element for each element in an array.
Postorder Traversal
Traverse binary tree in postorder (left, right, root)
Remove K Digits
Remove k digits from a number to make it as small as possible
Stock Span Problem
Calculate the span of stock prices for each day
Trapping Rain Water
Calculate how much rainwater can be trapped between bars of different heights
Valid Parentheses
Determine if the input string has valid brackets that are properly opened and closed
Valid Parentheses
Check if a string containing only parentheses is valid.