双指针

1023. Camelcase MatchingGiven an array of strings queries and a string pattern, return a boolean array answer where answer[i] is true if queries[i] matches pattern, and false otherwise. A query word queries[i] matches pattern if you can insert lowercase English letters into the pattern so that it equals the query. You may insert a character at any position in pattern or you may choose not to insert any characters at all. Example 1: 12345Input: queries =...

825. Friends Of Appropriate AgesThere are n persons on a social media website. You are given an integer array ages where ages[i] is the age of the ith person. A Person x will not send a friend request to a person y (x != y) if any of the following conditions is true: age[y] <= 0.5 * age[x] + 7 age[y] > age[x] age[y] > 100 && age[x] < 100 Otherwise, x will send a friend request to y. Note that if x sends a request to y, y will not necessarily send a request to x. Also, a...

826. Most Profit Assigning WorkYou have n jobs and m workers. You are given three arrays: difficulty, profit, and worker where: difficulty[i] and profit[i] are the difficulty and the profit of the ith job, and worker[j] is the ability of jth worker (i.e., the jth worker can only complete a job with difficulty at most worker[j]). Every worker can be assigned at most one job, but one job can be completed multiple times. For example, if three workers attempt the same job that pays $1, then...

611. Valid Triangle NumberGiven an integer array nums, return the number of triplets chosen from the array that can make triangles if we take them as side lengths of a triangle. Example 1: 123456Input: nums = [2,2,3,4]Output: 3Explanation: Valid combinations are: 2,3,4 (using the first 2)2,3,4 (using the second 2)2,2,3 Example 2: 12Input: nums = [4,2,3,4]Output: 4 题目大意给定一个整数数组 nums，返回数组中可作为三角形三条边长度的三元组数量。三角形三条边需满足：任意两边之和大于第三边。 核心解题思路：排序 + 双指针三角形三边的核心条件是：两边之和大于第三边。对于排序后的数组，可简化为： 设三条边为 a ≤...

189. 轮转数组给定一个整数数组 nums，将数组中的元素向右轮转 k 个位置，其中 k 是非负数。 示例 1: 123456输入: nums = [1,2,3,4,5,6,7], k = 3输出: [5,6,7,1,2,3,4]解释:向右轮转 1 步: [7,1,2,3,4,5,6]向右轮转 2 步: [6,7,1,2,3,4,5]向右轮转 3 步: [5,6,7,1,2,3,4] 示例 2: 12345输入：nums = [-1,-100,3,99], k = 2输出：[3,99,-1,-100]解释: 向右轮转 1 步: [99,-1,-100,3]向右轮转 2 步: [3,99,-1,-100] 题目大意给定一个整数数组 nums 和非负整数 k，将数组元素向右轮转 k 个位置（即每个元素向右移动 k 位，末尾元素移动到开头）。要求尽可能优化时间和空间复杂度。 核心解题思路：三次反转法常规思路（如临时数组、多次右移）要么空间复杂度高（O (n)），要么时间复杂度高（O (nk)）。三次反转法通过巧妙的反转操作，实现 O (n) 时间复杂度 + O (1)...

148. 排序链表给你链表的头结点 head ，请将其按 升序 排列并返回 排序后的链表 。 示例 1： 12输入：head = [4,2,1,3]输出：[1,2,3,4] 示例 2： 12输入：head = [-1,5,3,4,0]输出：[-1,0,3,4,5] 示例 3： 12输入：head = []输出：[] 题目大意给定链表的头节点 head，要求将链表按升序排列并返回排序后的链表头节点。 解题思路对于链表排序，最适合的高效算法是归并排序，原因如下： 归并排序的时间复杂度为 O (n log n)，是链表排序的最优选择 链表的归并操作不需要像数组那样额外分配 O (n)...

86. Partition ListGiven the head of a linked list and a value x, partition it such that all nodes less than x come before nodes greater than or equal to x. You should preserve the original relative order of the nodes in each of the two partitions. Example 1: 12Input: head = [1,4,3,2,5,2], x = 3Output: [1,2,2,4,3,5] Example 2: 12Input: head = [2,1], x = 2Output: [1,2] 题目大意给定链表的头节点 head 和一个值 x，要求将链表分隔成两部分：所有值小于 x 的节点排在所有值大于或等于 x...

82. Remove Duplicates from Sorted List IIGiven the head of a sorted linked list, delete all nodes that have duplicate numbers, leaving only distinct numbers from the original list. Return the linked list sorted as well. Example 1: 12Input: head = [1,2,3,3,4,4,5]Output: [1,2,5] Example 2: 12Input: head = [1,1,1,2,3]Output: [2,3] 题目大意给定一个已排序的链表，要求删除所有存在重复的节点（即重复的节点一个都不保留），仅保留原链表中只出现过一次的节点，最终返回排序后的新链表头节点。 核心解题思路由于链表已排序，重复节点必然相邻，因此可通过「遍历链表 + 跳过重复节点」的思路解决，关键是： 虚拟头节点：避免删除头节点时的特殊处理（如示例 2 中头节点...

287. Find the Duplicate NumberGiven an array of integers nums containing n + 1 integers where each integer is in the range [1, n] inclusive. There is only one repeated number in nums, return this repeated number. You must solve the problem without modifying the array nums and using only constant extra space. Example 1: 12Input: nums = [1,3,4,2,2]Output: 2 Example 2: 12Input: nums = [3,1,3,4,2]Output: 3 Example 3: 12Input: nums = [3,3,3,3,3]Output: 3 题目大意给定一个包含 n + 1 个整数的数组 nums，其中每个整数都在...

1089. Duplicate Zeros题目Given a fixed length array arr of integers, duplicate each occurrence of zero, shifting the remaining elements to the right. Note that elements beyond the length of the original array are not written. Do the above modifications to the input array in place, do not return anything from your function. Example 1: 123Input: [1,0,2,3,0,4,5,0]Output: nullExplanation: After calling your function, the input array is modified to: [1,0,0,2,3,0,0,4] Example 2: 123Input:...

922. Sort Array By Parity IIGiven an array of integers nums, half of the integers in nums are odd, and the other half are even. Sort the array so that whenever nums[i] is odd, i is odd, and whenever nums[i] is even, i is even. Return any answer array that satisfies this condition. Example 1: 123Input: nums = [4,2,5,7]Output: [4,5,2,7]Explanation: [4,7,2,5], [2,5,4,7], [2,7,4,5] would also have been accepted. Example 2: 12Input: nums = [2,3]Output: [2,3] 双指针解法： 初始化： 偶数索引指针 i 从 0 开始，每次移动 2...

977. Squares of a Sorted ArrayGiven an array of integers A sorted in non-decreasing order, return an array of the squares of each number, also in sorted non-decreasing order. Example 1: 12Input: [-4,-1,0,3,10]Output: [0,1,9,16,100] Example 2: 12Input: [-7,-3,2,3,11]Output: [4,9,9,49,121] Note: 1 <= A.length <= 10000 -10000 <= A[i] <= 10000 A is sorted in non-decreasing...

905. Sort Array By ParityGiven an integer array nums, move all the even integers at the beginning of the array followed by all the odd integers. Return any array that satisfies this condition. Example 1: 123Input: nums = [3,1,2,4]Output: [2,4,3,1]Explanation: The outputs [4,2,3,1], [2,4,1,3], and [4,2,1,3] would also be accepted. Example 2: 12Input: nums = [0]Output: [0] 解法1：双指针12345678910111213141516class Solution{public: vector<int> sortArrayByParity(vector<int>...

844. Backspace String Compare题目Given two strings S and T, return if they are equal when both are typed into empty text editors. # means a backspace character. Example 1: 123Input: S = "ab#c", T = "ad#c"Output: trueExplanation: Both S and T become "ac". Example 2: 123Input: S = "ab##", T = "c#d#"Output: trueExplanation: Both S and T become "". Example 3: 123Input: S = "a##c", T = "#a#c"Output: trueExplanation:...

283. Move Zeroes题目Given an array nums, write a function to move all 0's to the end of it while maintaining the relative order of the non-zero elements. Example 1: 12Input: [0,1,0,3,12]Output: [1,3,12,0,0] Note: You must do this in-place without making a copy of the array. Minimize the total number of operations. 解法1：双指针1234567891011121314151617181920class Solution {public: void moveZeroes(vector<int>& nums) { int n = nums.size(); int i = 0; //...

27. Remove Element给你一个数组 nums 和一个值 val，你需要 原地 移除所有数值等于 val 的元素。元素的顺序可能发生改变。然后返回 nums 中与 val 不同的元素的数量。 假设 nums 中不等于 val 的元素数量为 k，要通过此题，您需要执行以下操作： 更改 nums 数组，使 nums 的前 k 个元素包含不等于 val 的元素。nums 的其余元素和 nums 的大小并不重要。 返回 k。 用户评测： 评测机将使用以下代码测试您的解决方案： 123456789101112int[] nums = [...]; // 输入数组int val = ...; // 要移除的值int[] expectedNums = [...]; // 长度正确的预期答案。 // 它以不等于 val 的值排序。int k = removeElement(nums, val); // 调用你的实现assert k == expectedNums.length;sort(nums, 0, k); // 排序...

26. Remove Duplicates from Sorted Array给你一个 非严格递增排列 的数组 nums ，请你** 原地** 删除重复出现的元素，使每个元素 只出现一次 ，返回删除后数组的新长度。元素的 相对顺序 应该保持 一致 。然后返回 nums 中唯一元素的个数。 考虑 nums 的唯一元素的数量为 k ，你需要做以下事情确保你的题解可以被通过： 更改数组 nums ，使 nums 的前 k 个元素包含唯一元素，并按照它们最初在 nums 中出现的顺序排列。nums 的其余元素与 nums 的大小不重要。 返回 k 。 判题标准: 系统会用下面的代码来测试你的题解: 123456789int[] nums = [...]; // 输入数组int[] expectedNums = [...]; // 长度正确的期望答案int k = removeDuplicates(nums); // 调用assert k == expectedNums.length;for (int i = 0; i < k; i++) { assert...

16. 3Sum Closest题目Given an array nums of n integers and an integer target, find three integers in nums such that the sum is closest to target. Return the sum of the three integers. You may assume that each input would have exactly one solution. Example: 123Given array nums = [-1, 2, 1, -4], and target = 1.The sum that is closest to the target is 2. (-1 + 2 + 1 = 2). 题目大意给定一个数组，要求在这个数组中找出 3 个数之和离 target 最近。 解题思路 初始值优化： 原代码中it初始化为...