Given a linked list, swap every two adjacent nodes and return its head. You must solve the problem without modifying the values in the list's nodes (i.e., only nodes themselves may be changed.)   Example 1: Input: head = [1,2,3,4] Output: [2,1,4,3] Example…

给你两个 非空 的链表，表示两个非负的整数。它们每位数字都是按照 逆序 的方式存储的，并且每个节点只能存储 一位 数字。 请你将两个数相加，并以相同形式返回一个表示和的链表。 你可以假设除了数字 0 之外，这两个数都不会以 0 开头。   示例 1： 输入：l1 = [2,4,3], l2 = [5,6,4] 输出：[7,0,8] 解释：342 + 465 = 807. 示例 2： 输入：l1 = [0], l2 = [0] 输出：[0] 示例 3： 输入：l1 = [9,9,9,9,9,9,9], l2…

Given an integer n, return a list of all possible full binary trees with n nodes. Each node of each tree in the answer must have Node.val == 0. Each element of the answer is the root node of one possible tree. You may return the final list of trees in any…

Implement pow(x, n), which calculates x raised to the power n (i.e., xn).   Example 1: Input: x = 2.00000, n = 10 Output: 1024.00000 Example 2: Input: x = 2.10000, n = 3 Output: 9.26100 Example 3: Input: x = 2.00000, n = -2 Output: 0.25000 Explanation: 2…

You are given an integer array nums. Two players are playing a game with this array: player 1 and player 2. Player 1 and player 2 take turns, with player 1 starting first. Both players start the game with a score of 0. At each turn, the player takes one of…

给定一个单链表 L 的头节点 head ，单链表 L 表示为： L0 → L1 → … → Ln - 1 → Ln 请将其重新排列后变为： L0 → Ln → L1 → Ln - 1 → L2 → Ln - 2 → … 不能只是单纯的改变节点内部的值，而是需要实际的进行节点交换。   示例 1： 输入：head = [1,2,3,4] 输出：[1,4,2,3] 示例 2： 输入：head = [1,2,3,4,5] 输出：[1,5,2,4,3]   提示：

将两个升序链表合并为一个新的 升序 链表并返回。新链表是通过拼接给定的两个链表的所有节点组成的。    示例 1： 输入：l1 = [1,2,4], l2 = [1,3,4] 输出：[1,1,2,3,4,4] 示例 2： 输入：l1 = [], l2 = [] 输出：[] 示例 3： 输入：l1 = [], l2 = [0] 输出：[0]   提示：

给你一个链表，两两交换其中相邻的节点，并返回交换后链表的头节点。你必须在不修改节点内部的值的情况下完成本题（即，只能进行节点交换）。   示例 1： 输入：head = [1,2,3,4] 输出：[2,1,4,3] 示例 2： 输入：head = [] 输出：[] 示例 3： 输入：head = [1] 输出：[1]   提示：

Given an integer n, return true if it is a power of four. Otherwise, return false. An integer n is a power of four, if there exists an integer x such that n == 4x.   Example 1: Input: n = 16 Output: true Example 2: Input: n = 5 Output: false Example 3: Input:…

We build a table of n rows (1-indexed). We start by writing 0 in the 1st row. Now in every subsequent row, we look at the previous row and replace each occurrence of 0 with 01, and each occurrence of 1 with 10.