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使用两个队列存储二叉树，主队列循环遍历各层，临时队列对每一层元素遍历，代码如下，res存放层序遍历结果：class Solution: def levelOrder(self, root: TreeNode) -> List[List[int]]: if not root: return [] queue = [root] #主队列 res = [] level = 0 #标记层号

​在树的深度优先遍历中（包括前序、中序、后序遍历），递归方法最为直观易懂，但考虑到效率，我们通常不推荐使用递归。栈迭代方法虽然提高了效率，但其嵌套循环却非常烧脑，不易理解，容易造成“一看就懂，一写就废”的窘况。而且对于不同的遍历顺序（前序、中序、后序），循环结构差异很大，更增加了记忆负担。因此，我在这里介绍一种“灰白标记法”，兼具栈迭代方法的高效，又像递归方法一样简洁易懂，更重要的是，这种方法对于前序、中序、后序遍历，能够写出完全一致的代码。其核心思想如下：使用颜色标记节点的状态，新节点为白色，已

填充每个节点的下一个右侧节点指针 II难度中等给定一个二叉树struct Node { int val; Node *left; Node *right; Node *next;}填充它的每个 next 指针，让这个指针指向其下一个右侧节点。如果找不到下一个右侧节点，则将 next 指针设置为 NULL。初始状态下，所有 next 指针都被设置为 NULL。进阶：你只能使用常量级额外空间。使用递归解题也符合要求，本题中递归程序占用的栈空间不算做额外的空间复杂度。示.

A Binary Search Tree (BST) is recursively defined as a binary tree which has the following properties:The left subtree of a node contains only nodes with keys less than or equal to the node's key. ...

The following is from Max Howell @twitter:Google: 90% of our engineers use the software you wrote (Homebrew), but you can't invert a binary tree on a whiteboard so fuck off.Now it's your turn to...

Suppose that all the keys in a binary tree are distinct positive integers. A unique binary tree can be determined by a given pair of postorder and inorder traversal sequences, or preorder and inorder ...

A supply chain is a network of retailers（零售商）, distributors（经销商）, and suppliers（供应商）-- everyone involved in moving a product from supplier to customer.Starting from one root supplier, everyone on th...

An AVL tree is a self-balancing binary search tree. In an AVL tree, the heights of the two child subtrees of any node differ by at most one; if at any time they differ by more than one, rebalancing is...

Suppose that all the keys in a binary tree are distinct positive integers. A unique binary tree can be determined by a given pair of postorder and inorder traversal sequences. And it is a simple stand...

Given a syntax tree (binary), you are supposed to output the corresponding infix expression, with parentheses reflecting the precedences of the operators.Input Specification:Each input file contai...

The lowest common ancestor (LCA) of two nodes U and V in a tree is the deepest node that has both U and V as descendants.A binary search tree (BST) is recursively defined as a binary tree which has ...

There is a kind of balanced binary search tree named red-black tree in the data structure. It has the following 5 properties:(1) Every node is either red or black. (2) The root is black. (3) Every...

Suppose that all the keys in a binary tree are distinct positive integers. Given the preorder and inorder traversal sequences, you are supposed to output the first number of the postorder traversal se...

A Binary Search Tree (BST) is recursively defined as a binary tree which has the following properties:The left subtree of a node contains only nodes with keys less than the node's key. The right su...

A supply chain is a network of retailers（零售商）, distributors（经销商）, and suppliers（供应商）-- everyone involved in moving a product from supplier to customer.Starting from one root supplier, everyone on th...

You need to construct a string consists of parenthesis and integers from a binary tree with the preorder traversing way.The null node needs to be represented by empty parenthesis pair "()". And you ne...

A family hierarchy is usually presented by a pedigree tree. Your job is to count those family members who have no child.InputEach input file contains one test case. Each case starts with a line co...

Suppose that all the keys in a binary tree are distinct positive integers. Given the postorder and inorder traversal sequences, you are supposed to output the level order traversal sequence of the cor...

1043 Is It a Binary Search Tree（25 分）A Binary Search Tree (BST) is recursively defined as a binary tree which has the following properties:The left subtree of a node contains only nodes with keys ...

1147 Heaps（30 分）In computer science, a heap is a specialized tree-based data structure that satisfies the heap property: if P is a parent node of C, then the key (the value) of P is either greater t...

1151 LCA in a Binary Tree（30 分）The lowest common ancestor (LCA) of two nodes U and V in a tree is the deepest node that has both U and V as descendants.Given any two nodes in a binary tree, you ar...

A Binary Search Tree (BST) is recursively defined as a binary tree which has the following properties:The left subtree of a node contains only nodes with keys less than the node's key. The right su...

Given a non-empty tree with root RRR, and with weight WiW_iW​i​​ assigned to each tree node TiT_iT​i​​. The weight of a path from RRR to LLL is defined to be the sum of the weights of all the nodes al...

An AVL tree is a self-balancing binary search tree. In an AVL tree, the heights of the two child subtrees of any node differ by at most one; if at any time they differ by more than one, rebalancing is...

An inorder binary tree traversal can be implemented in a non-recursive way with a stack. For example, suppose that when a 6-node binary tree (with the keys numbered from 1 to 6) is traversed, the stac...

Given a tree, you are supposed to tell if it is a complete binary tree.Input Specification:Each input file contains one test case. For each case, the first line gives a positive integer N (≤20) wh...

A supply chain is a network of retailers（零售商）, distributors（经销商）, and suppliers（供应商）-- everyone involved in moving a product from supplier to customer.Starting from one root supplier, everyone on th...

A family hierarchy is usually presented by a pedigree tree where all the nodes on the same level belong to the same generation. Your task is to find the generation with the largest population.Input ...

Given two binary trees and imagine that when you put one of them to cover the other, some nodes of the two trees are overlapped while the others are not. You need to merge them into a new binary tree....