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173. Binary Search Tree Iterator Implement an iterator over a binary search tree (BST). Your iterator will be initialized with the root node of a BST. Calling next() will return the next small

331. Verify Preorder Serialization of a Binary Tree One way to serialize a binary tree is to use pre-order traversal. When we encounter a non-null node, we record the node's value. If it is a nul

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

Given a sequence of n integers a1, a2, ..., an, a 132 pattern is a subsequence ai, aj, ak such that i j k and ai k j. Design an algorithm that takes a list of n numbers as input and checks whethe

//迷宫问题：求迷宫中从入口到出口的一条路径 //通常用的是“穷举求解”的方法，即从入口出发，顺某一方向向前探索，若能走通，则继续向前走； //否则沿着原路返回，换一个方向再继续探索，直至所有可能的通路都探索到为止 //为了保证在任何位置上都能沿着原路返回，需要用一个先进先出的堆栈结构来保存从入口到当前位置的路径 /* 可以简单描述如下： do{ 若当前位置可通， 则{

150. Evaluate Reverse Polish Notation Evaluate the value of an arithmetic expression in Reverse Polish Notation. Valid operators are +, -, *, /. Each operand may be an integer or another expressi

iven a string containing just the characters '(' and ')', find the length of the longest valid (well-formed) parentheses substring. For "(()", the longest valid parentheses substring is "()", w

Given n non-negative integers representing the histogram's bar height where the width of each bar is 1, find the area of largest rectangle in the histogram. Above is a histogram where width o