Leetcode 0826. Most Profit Assigning Work
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 th...
Leetcode 0012. Integer to Roman (python)
12. Integer to Roman题目Roman numerals are represented by seven different symbols: I, V, X, L, C, D and M. 12345678Symbol ValueI 1V 5X 10L 50C 100D 500M 1000 For example, 2 is written as II in Roman numeral, just two one's added together. 12 is written as XII, which is simply X + II. The number 27 is written as XXVII, which is XX + V + II. Roman numerals are usually written largest to smallest from le...
Leetcode 0825. Friends Of Appropriate Ages
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 ...
Leetcode 0011. Container With Most Water (python)
11. Container With Most Water题目You are given an integer array height of length n. There are n vertical lines drawn such that the two endpoints of the i-th line are (i, 0) and (i, height[i]). Find two lines that together with the x-axis form a container, such that the container contains the most water. Return the maximum amount of water a container can store. Notice that you may not slant the container. Example 1: 1234Input: height = [1,8,6,2,5,4,8,3,7]Output: 49Explanation: The above vertical...
Leetcode 0707. Design Linked List
707. Design Linked ListDesign your implementation of the linked list. You can choose to use a singly or doubly linked list.A node in a singly linked list should have two attributes: val and next. val is the value of the current node, and next is a pointer/reference to the next node.If you want to use the doubly linked list, you will need one more attribute prev to indicate the previous node in the linked list. Assume all nodes in the linked list are 0-indexed. Implement the MyLinkedList ...
Leetcode 0704. Binary Search
704. Binary Search题目Given a sorted (in ascending order) integer array nums of n elements and a target value, write a function to search target in nums. If target exists, then return its index, otherwise return -1. Example 1: Input: nums = [-1,0,3,5,9,12], target = 9 Output: 4 Explanation: 9 exists in nums and its index is 4 Example 2: Input: nums = [-1,0,3,5,9,12], target = 2 Output: -1 Explanation: 2 does not exist in nums so return -1 Note: You may assume that all elements in nums are un...
Leetcode 0010. Regular Expression Matching (python)
10. Regular Expression Matching题目Given an input string s and a pattern p, implement regular expression matching with support for '.' and '*' where: '.' Matches any single character. '*' Matches zero or more of the preceding element. The matching should cover the entire input string (not partial). Example 1: 123Input: s = "aa", p = "a"Output: falseExplanation: "a" does not match the entire string "aa". Example 2: 123Inp...
Leetcode 0637. Average of Levels in Binary Tree
637. Average of Levels in Binary TreeGiven the root of a binary tree, return the average value of the nodes on each level in the form of an array. Answers within 10-5 of the actual answer will be accepted. Example 1: 1234Input: root = [3,9,20,null,null,15,7]Output: [3.00000,14.50000,11.00000]Explanation: The average value of nodes on level 0 is 3, on level 1 is 14.5, and on level 2 is 11.Hence return [3, 14.5, 11]. Example 2: 12Input: root = [3,9,20,15,7]Output: [3.00000,14.50000,11.00000...
Leetcode 0009. Palindrome Number (python)
9. Palindrome Number题目Given an integer x, return true if x is a palindrome, and false otherwise. Example 1: 123Input: x = 121Output: trueExplanation: 121 reads as 121 from left to right and from right to left. Example 2: 123Input: x = -121Output: falseExplanation: From left to right, it reads -121. From right to left, it becomes 121-. Therefore it is not a palindrome. Example 3: 123Input: x = 10Output: falseExplanation: Reads 01 from right to left. Therefore it is not a palindrome. Constra...
Leetcode 0626. 换座位
626. 换座位表: Seat 123456789+-------------+---------+| Column Name | Type |+-------------+---------+| id | int || student | varchar |+-------------+---------+id 是该表的主键（唯一值）列。该表的每一行都表示学生的姓名和 ID。ID 序列始终从 1 开始并连续增加。 编写解决方案来交换每两个连续的学生的座位号。如果学生的数量是奇数，则最后一个学生的id不交换。 按 id 升序 返回结果表。 查询结果格式如下所示。 示例 1: 1234567891011121314151617181920212223输入: Seat 表:+----+---------+| id | student |+----+---------+| 1 | Abbot || 2 | Doris || 3 | Emerson || 4 | Green || 5 | Jeames |+----+---...
Leetcode 0611. Valid Triangle Number
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 ≤ b...
Leetcode 0008. String to Integer (atoi) (python)
8. String to Integer (atoi)题目Implement the myAtoi(string s) function, which converts a string to a 32-bit signed integer. The algorithm for myAtoi(string s) is as follows: Whitespace: Ignore any leading whitespace (" "). Signedness: Determine the sign by checking if the next character is '-' or '+', assuming positivity if neither present. Conversion: Read the integer by skipping leading zeros until a non-digit character is encountered or the end of the string is rea...
Leetcode 0572. Subtree of Another Tree
572. Subtree of Another TreeGiven the roots of two binary trees root and subRoot, return true if there is a subtree of root with the same structure and node values of subRoot and false otherwise. A subtree of a binary tree tree is a tree that consists of a node in tree and all of this node's descendants. The tree tree could also be considered as a subtree of itself. Example 1: 12Input: root = [3,4,5,1,2], subRoot = [4,1,2]Output: true Example 2: 12Input: root = [3,4,5,1,2,null,null,nu...
Leetcode 0007. Reverse Integer (python)
7. Reverse Integer题目Given a signed 32-bit integer x, return x with its digits reversed. If reversing x causes the value to go outside the signed 32-bit integer range [-2³¹, 2³¹ - 1], then return 0. Assume the environment does not allow you to store 64-bit integers (signed or unsigned). Example 1: 12Input: x = 123Output: 321 Example 2: 12Input: x = -123Output: -321 Example 3: 12Input: x = 120Output: 21 Constraints: -2³¹ <= x <= 2³¹ - 1 题目大意将一个 32 位有符号整数的数字部分反转。如果反转后的整数溢出 32 位有符号整数范围...
Leetcode 0570. 至少有5名直接下属的经理
570. 至少有5名直接下属的经理表: Employee 123456789101112+-------------+---------+| Column Name | Type |+-------------+---------+| id | int || name | varchar || department | varchar || managerId | int |+-------------+---------+id 是此表的主键（具有唯一值的列）。该表的每一行表示雇员的名字、他们的部门和他们的经理的id。如果managerId为空，则该员工没有经理。没有员工会成为自己的管理者。 编写一个解决方案，找出至少有五个直接下属的经理。 以 任意顺序 返回结果表。 查询结果格式如下所示。 示例 1: 123456789101112131415161718输入: Employee 表:+-----+-------+------------+-----------+| id | name | department ...
Leetcode 0006. Zigzag Conversion (python)
6. Zigzag Conversion题目The string "PAYPALISHIRING" is written in a zigzag pattern on a given number of rows like this: (you may want to display this pattern in a fixed font for better legibility) 123P A H NA P L S I I GY I R And then read line by line: "PAHNAPLSIIGYIR" Write the code that will take a string and make this conversion given a number of rows: 1string convert(string s, int numRows); Example 1: 12Input: s = "PAYPALISHIRING", numRows = 3Outpu...
Leetcode 0515. Find Largest Value in Each Tree Row
515. Find Largest Value in Each Tree RowGiven the root of a binary tree, return an array of the largest value in each row of the tree (0-indexed). Example 1: 12Input: root = [1,3,2,5,3,null,9]Output: [1,3,9] Example 2: 12Input: root = [1,2,3]Output: [1,3] 题目大意给定一棵二叉树的根节点 root，返回一个数组，其中每个元素是二叉树对应行（从 0 开始索引）中的最大值。 例如： 输入二叉树 [1,3,2,5,3,null,9]，第 0 行最大值为 1，第 1 行最大值为 3，第 2 行最大值为 9，因此返回 [1,3,9]。 解题思路要找到每一行的最大值，核心是按层遍历二叉树，并在遍历过程中记录每层的最大值。具体步骤如下： 层序遍历初始化：若根节点为空，直接返回空数组；否则将根节点入队。 逐层处理节点： 记录当前队列...
Leetcode 0513. Find Bottom Left Tree Value
513. Find Bottom Left Tree ValueGiven the root of a binary tree, return the leftmost value in the last row of the tree. Example 1: 12Input: root = [2,1,3]Output: 1 Example 2: 12Input: root = [1,2,3,4,null,5,6,null,null,7]Output: 7 题目大意给定一棵二叉树的根节点 root，返回树的最后一行中最左边的节点值。即需要找到二叉树最深一层的最左侧节点的值。 例如： 输入二叉树 [2,1,3]，最深层是第 2 层，最左侧节点值为 1，返回 1； 输入二叉树 [1,2,3,4,null,5,6,null,null,7]，最深层是第 4 层，最左侧节点值为 7，返回 7。 解题思路找到树左下角的值，关键是确定最深层和该层的最左侧节点。主要有两种实现方法： 1. 层序遍历（BFS） 按层遍历二叉树，记录每一层的第一个节点值； 最后一层的第一个节点值即为结果...
Leetcode 0005. Longest Palindromic Substring (python)
5. Longest Palindromic Substring题目Given a string s, return the longest palindromic substring in s. Example 1: 123Input: s = "babad"Output: "bab"Explanation: "aba" is also a valid answer. Example 2: 12Input: s = "cbbd"Output: "bb" Constraints: 1 <= s.length <= 1000 s consist of only digits and English letters. 题目大意在给定字符串中找出最长的回文子串（palindromic substring）。回文串是指正读反读都一样的字符串。若存在多个等长的最长回文子串，返回任意一个即可。字符串长度上限为 1000，仅包含数字和英文字母。 你选用何种方法解题？本题的核...
Leetcode 0509. Fibonacci Number
509. Fibonacci Number题目The Fibonacci numbers, commonly denoted F(n) form a sequence, called the Fibonacci sequence, such that each number is the sum of the two preceding ones, starting from 0 and 1. That is, F(0) = 0, F(1) = 1 F(N) = F(N - 1) + F(N - 2), for N > 1. Given N, calculate F(N). Example 1: Input: 2 Output: 1 Explanation: F(2) = F(1) + F(0) = 1 + 0 = 1. Example 2: Input: 3 Output: 2 Explanation: F(3) = F(2) + F(1) = 1 + 1 = 2. Example 3: Input: 4 Output: 3 Explanation: F(4) ...
Leetcode 0004. Median of Two Sorted Arrays (python)
4. Median of Two Sorted Arrays题目Given two sorted arrays nums1 and nums2 of size m and n respectively, return the median of the two sorted arrays. The overall run time complexity should be O(log (m+n)). Example 1: 123Input: nums1 = [1,3], nums2 = [2]Output: 2.00000Explanation: merged array = [1,2,3] and median is 2. Example 2: 123Input: nums1 = [1,2], nums2 = [3,4]Output: 2.50000Explanation: merged array = [1,2,3,4] and median is (2 + 3) / 2 = 2.5. 题目大意给定两个已排序的数组 nums1 和 nums2，找出这两个有序数组的中位数。...
Leetcode 0503. 下一个更大元素 II
503. 下一个更大元素 II给定一个循环数组 nums （ nums[nums.length - 1] 的下一个元素是 nums[0] ），返回 nums 中每个元素的 下一个更大元素 。 数字 x 的 下一个更大的元素 是按数组遍历顺序，这个数字之后的第一个比它更大的数，这意味着你应该循环地搜索它的下一个更大的数。如果不存在，则输出 -1 。 示例 1: 12345输入: nums = [1,2,1]输出: [2,-1,2]解释: 第一个 1 的下一个更大的数是 2；数字 2 找不到下一个更大的数； 第二个 1 的下一个最大的数需要循环搜索，结果也是 2。 示例 2: 12输入: nums = [1,2,3,4,3]输出: [2,3,4,-1,4] 解题思路核心思路是单调栈 + 数组翻倍模拟循环，通过将数组复制一份拼接在末尾（模拟循环），利用单调栈高效找到每个元素的下一个更大元素： 模拟循环数组： 将原数组 nums 复制一份并拼接在末尾（如 [1,2,1] 变为 [1,2,1,1,2,1]），这样无需额外处理循环边界，可直接线性遍历。 单调栈求解： 使用单调栈存储...
Leetcode 0496. 下一个更大元素 I
496. 下一个更大元素 Inums1 中数字 x 的 下一个更大元素 是指 x 在 nums2 中对应位置 右侧 的 第一个 比 x 大的元素。 给你两个 没有重复元素 的数组 nums1 和 nums2 ，下标从 0 开始计数，其中nums1 是 nums2 的子集。 对于每个 0 <= i < nums1.length ，找出满足 nums1[i] == nums2[j] 的下标 j ，并且在 nums2 确定 nums2[j] 的 下一个更大元素 。如果不存在下一个更大元素，那么本次查询的答案是 -1 。 返回一个长度为 nums1.length 的数组 ans 作为答案，满足 ans[i] 是如上所述的 下一个更大元素 。 示例 1： 123456输入：nums1 = [4,1,2], nums2 = [1,3,4,2].输出：[-1,3,-1]解释：nums1 中每个值的下一个更大元素如下所述：- 4 ，用加粗斜体标识，nums2 = [1,3,4,2]。不存在下一个更大元素，所以答案是 -1 。- 1 ，用加粗斜体标识，nums2 = [1,3,4,2...
Leetcode 0491. Non-decreasing Subsequences
491. Non-decreasing SubsequencesGiven an integer array nums, return all the different possible non-decreasing subsequences of the given array with at least two elements. You may return the answer in any order. Example 1: 12Input: nums = [4,6,7,7]Output: [[4,6],[4,6,7],[4,6,7,7],[4,7],[4,7,7],[6,7],[6,7,7],[7,7]] Example 2: 12Input: nums = [4,4,3,2,1]Output: [[4,4]] 题目大意给定一个整数数组 nums，返回所有不同的、长度至少为 2 的非递减子序列。子序列是由数组派生而来的序列，删除（或不删除）数组中的元素而不改变其余元素的顺序。 例如： 输入 nums = [4,6,7,7]，输出包含 [4,6]、[4,6,7...
Leetcode 0003. Longest Substring Without Repeating Characters (python)
3. Longest Substring Without Repeating Characters题目Given a string s, find the length of the longest substring without repeating characters. Example 1: 123Input: s = "abcabcbb"Output: 3Explanation: The answer is "abc", with the length of 3. Example 2: 123Input: s = "bbbbb"Output: 1Explanation: The answer is "b", with the length of 1. Example 3: 1234Input: s = "pwwkew"Output: 3Explanation: The answer is "wke", with the length of 3.No...
