给你一棵 完美 二叉树的根节点 root ，请你反转这棵树中每个 奇数 层的节点值。

Given the root node of a binary search tree and two integers low and high, return the sum of values of all nodes with a value in the inclusive range [low, high].   Example 1: Input: root = [10,5,15,3,7,null,18], low = 7, high = 15 Output: 32 Explanation:…

Consider all the leaves of a binary tree, from left to right order, the values of those leaves form a leaf value sequence. For example, in the given tree above, the leaf value sequence is (6, 7, 4, 9, 8). Two binary trees are considered leaf-similar if their…

You are given the root of a binary tree with unique values, and an integer start. At minute 0, an infection starts from the node with value start. Each minute, a node becomes infected if:

Given the root of a binary tree, find the maximum value v for which there exist different nodes a and b where v = |a.val - b.val| and a is an ancestor of b. A node a is an ancestor of b if either: any child of a is equal to b or any child of a is an ancestor…

Given a binary tree where node values are digits from 1 to 9. A path in the binary tree is said to be pseudo-palindromic if at least one permutation of the node values in the path is a palindrome. Return the number of pseudo-palindromic paths going from the…

Given a binary tree with the following rules:

We run a preorder depth-first search (DFS) on the root of a binary tree. At each node in this traversal, we output D dashes (where D is the depth of this node), then we output the value of this node.  If the depth of a node is D, the depth of its immediate…

Given two integer arrays, preorder and postorder where preorder is the preorder traversal of a binary tree of distinct values and postorder is the postorder traversal of the same tree, reconstruct and return the binary tree. If there exist multiple answers…

给你一个有根节点 root 的二叉树，返回它 最深的叶节点的最近公共祖先 。 回想一下：

Given the root of a binary tree, return the lowest common ancestor of its deepest leaves. Recall that:

给你一个二叉树的根节点 root。设根节点位于二叉树的第 1 层，而根节点的子节点位于第 2 层，依此类推。 返回总和 最大 的那一层的层号 x。如果有多层的总和一样大，返回其中 最小 的层号 x。   示例 1： 输入：root = [1,7,0,7,-8,null,null] 输出：2 解释： 第 1 层各元素之和为 1， 第 2 层各元素之和为 7 + 0 = 7， 第 3 层各元素之和为 7 + -8 = -1， 所以我们返回第 2 层的层号，它的层内元素之和最大。 示例 2： 输入：root =…

Given the root of a binary tree, the level of its root is 1, the level of its children is 2, and so on. Return the smallest level x such that the sum of all the values of nodes at level x is maximal.   Example 1: Input: root = [1,7,0,7,-8,null,null] Output:…

给你一棵二叉树，它的根为 root 。请你删除 1 条边，使二叉树分裂成两棵子树，且它们子树和的乘积尽可能大。 由于答案可能会很大，请你将结果对 10^9 + 7 取模后再返回。   示例 1： 输入：root = [1,2,3,4,5,6] 输出：110 解释：删除红色的边，得到 2 棵子树，和分别为 11 和 10 。它们的乘积是 110 （11*10） 示例 2： 输入：root = [1,null,2,3,4,null,null,5,6] 输出：90 解释：移除红色的边，得到 2 棵子树，和分别是…

Given the root of a binary tree, split the binary tree into two subtrees by removing one edge such that the product of the sums of the subtrees is maximized. Return the maximum product of the sums of the two subtrees. Since the answer may be too large, return…

给定一个根为 root 的二叉树，每个节点的深度是 该节点到根的最短距离 。 返回包含原始树中所有 最深节点 的 最小子树 。 如果一个节点在 整个树 的任意节点之间具有最大的深度，则该节点是 最深的 。 一个节点的 子树 是该节点加上它的所有后代的集合。   示例 1： 输入：root = [3,5,1,6,2,0,8,null,null,7,4] 输出：[2,7,4] 解释： 我们返回值为 2 的节点，在图中用黄色标记。 在图中用蓝色标记的是树的最深的节点。 注意，节点 5、3 和 2 包含树中最深的节点，但节点…

Given the root of a binary tree, the depth of each node is the shortest distance to the root. Return the smallest subtree such that it contains all the deepest nodes in the original tree. A node is called the deepest if it has the largest depth possible among…

给定一个二叉树，判断它是否是 平衡二叉树     示例 1： 输入：root = [3,9,20,null,null,15,7] 输出：true 示例 2： 输入：root = [1,2,2,3,3,null,null,4,4] 输出：false 示例 3： 输入：root = [] 输出：true   提示：

Given a binary tree, determine if it is height-balanced.   Example 1: Input: root = [3,9,20,null,null,15,7] Output: true Example 2: Input: root = [1,2,2,3,3,null,null,4,4] Output: false Example 3: Input: root = [] Output: true   Constraints:

给你一棵二叉搜索树，请你返回一棵 平衡后 的二叉搜索树，新生成的树应该与原来的树有着相同的节点值。如果有多种构造方法，请你返回任意一种。 如果一棵二叉搜索树中，每个节点的两棵子树高度差不超过 1 ，我们就称这棵二叉搜索树是 平衡的 。   示例 1： 输入：root = [1,null,2,null,3,null,4,null,null] 输出：[2,1,3,null,null,null,4] 解释：这不是唯一的正确答案，[3,1,4,null,2,null,null] 也是一个可行的构造方案。 示例 2：…

Given the root of a binary search tree, return a balanced binary search tree with the same node values. If there is more than one answer, return any of them. A binary search tree is balanced if the depth of the two subtrees of every node never differs by…