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236. Lowest Common Ancestor of a Binary Tree Given a binary tree, find the lowest common ancestor (LCA) of two given nodes in the tree. According to the definition of LCA on Wikipedia: “The lo

341. Flatten Nested List Iterator Given a nested list of integers, implement an iterator to flatten it. Each element is either an integer, or a list -- whose elements may also be integers or o

297. Serialize and Deserialize Binary Tree Serialization is the process of converting a data structure or object into a sequence of bits so that it can be stored in a file or memory buffer, or tr

Implement regular expression matching with support for '.' and '*'. '.' Matches any single character. '*' Matches zero or more of the preceding element. The matching should cover the entire input st

Given a complete binary tree, count the number of nodes.Definition of a complete binary tree from Wikipedia: In a complete binary tree every level, except possibly the last, is completely filled, and

You need to construct a binary tree from a string consisting of parenthesis and integers.The whole input represents a binary tree. It contains an integer followed by zero, one or two pairs of parenthes