A critical point in a linked list is defined as either a local maxima or a local minima. A node is a local maxima if the current node has a value strictly greater than the previous node and the next node. A node is a local minima if the current node has a…

给你一个 m x n 的网格图 classroom，其中一个学生志愿者负责清理散布在教室里的垃圾。网格图中的每个单元格是以下字符之一：

You are given an m x n grid classroom where a student volunteer is tasked with cleaning up litter scattered around the room. Each cell in the grid is one of the following:

给你一个长度为 n 的数组 nums1，其中包含 互不相同 的整数。 你需要构造另一个长度为 n 的数组 nums2，使得 nums2 中的元素要么全部为 奇数，要么全部为 偶数。 对于每个下标 i，你必须从以下两种选择中 任选其一（顺序不限）：

You are given an array nums1 of n distinct integers. You want to construct another array nums2 of length n such that the elements in nums2 are either all odd or all even. For each index i, you must choose exactly one of the following (in any order):

给你一个长度为 n 的数组 nums1，其中包含 互不相同 的整数。

You are given an array nums1 of n distinct integers. You want to construct another array nums2 of length n such that the elements in nums2 are either all odd or all even. For each index i, you must choose exactly one of the following (in any order):

给你一个长度为 n 的整数数组 nums 和一个整数 k。 对于每个下标 i，定义它的 不稳定值 为 max(nums[0..i]) - min(nums[i..n - 1])。 换句话说：

You are given an integer array nums of length n and an integer k. For each index i, define its instability score as max(nums[0..i]) - min(nums[i..n - 1]). In other words:

给你一个长度为 n 的整数数组 nums 和一个整数 k。

You are given an integer array nums of length n and an integer k. For each index i, define its instability score as max(nums[0..i]) - min(nums[i..n - 1]). In other words:

给你两个字符串 s 和 t ，统计并返回在 s 的 子序列 中 t 出现的个数。 测试用例保证结果在 32 位有符号整数范围内。   示例 1： 输入：s = "rabbbit", t = "rabbit"输出：3解释： 如下所示, 有 3 种可以从 s 中得到 "rabbit" 的方案。 rabbbit rabbbit rabbbit 示例 2： 输入：s = "babgbag", t = "bag" 输出：5解释： 如下所示, 有 5 种可以从 s 中得到 "bag" 的方案。 babgbag babgbag…

Given two strings s and t, return the number of distinct subsequences of s which equals t. The test cases are generated so that the answer fits on a 32-bit signed integer.   Example 1: Input: s = "rabbbit", t = "rabbit" Output: 3 Explanation: As shown below…

给定一个字符串 s，计算 s 的 不同非空子序列 的个数。因为结果可能很大，所以返回答案需要对 10^9 + 7 取余 。 字符串的 子序列 是经由原字符串删除一些（也可能不删除）字符但不改变剩余字符相对位置的一个新字符串。

Given a string s, return the number of distinct non-empty subsequences of s. Since the answer may be very large, return it modulo 109 + 7.

给你一个整数 n。 返回将所有从 [1, n]（包含两端）范围内的整数以 标准 数字格式书写时所用到的 逗号总数。 在 标准 格式中：

You are given an integer n. Return the total number of commas used when writing all integers from [1, n] (inclusive) in standard number formatting. In standard formatting:

给你一个整数 n。

You are given an integer n. Return the total number of commas used when writing all integers from [1, n] (inclusive) in standard number formatting. In standard formatting:

给你一棵二叉树的根节点 root ，找出并返回满足要求的节点数，要求节点的值等于其 子树 中值的 平均值 。 注意：

Given the root of a binary tree, return the number of nodes where the value of the node is equal to the average of the values in its subtree. Note: