Leetcode

2462. Total Cost to Hire K Hardness: \(\color{orange}\textsf{Medium}\) Ralated Topics: Array、Two Pointer、Heap (Priority Queue)、Simulation \(\color{blue}\textsf{Weekly Contest 318}\) 一、題目 You are given a 0-indexed integer array costs where costs[i] is the cost of hiring the ith worker. You are also given two integers k and candidates. We want to hire exactly k workers according to the following rules: You will run k sessions and hire exactly one worker in each session. In each hiring session, choose the worker with the lowest cost from either the first candidates workers or the last candidates workers. Break the tie by the smallest index. For example, if costs = [3,2,7,7,1,2] and candidates = 2, then in the first hiring session, we will choose the 4th worker because they have the lowest cost [3,2,7,7,1,2]. In the second hiring session, we will choose 1st worker because they have the same lowest cost as 4th worker but they have the smallest index [3,2,7,7,2]. Please note that the indexing may be changed in the process. If there are fewer than candidates workers remaining, choose the worker with the lowest cost among them. Break the tie by the smallest index. A worker can only be chosen once. Return the total cost to hire exactly k workers. Example 1: ...

2461. Maximum Sum of Distinct Subarrays With Length K Hardness: \(\color{orange}\textsf{Medium}\) Ralated Topics: Array、Hash Table、Sliding Window \(\color{blue}\textsf{Weekly Contest 318}\) 一、題目 You are given an integer array nums and an integer k. Find the maximum subarray sum of all the subarrays of nums that meet the following conditions: The length of the subarray is k, and All the elements of the subarray are distinct. Return the maximum subarray sum of all the subarrays that meet the conditions. If no subarray meets the conditions, return 0. A subarray is a contiguous non-empty sequence of elements within an array. Example 1: ...

2460. Apply Operations to an Array Hardness: \(\color{green}\textsf{Easy}\) Ralated Topics: Array、Simulation \(\color{blue}\textsf{Weekly Contest 318}\) 一、題目 You are given a 0-indexed array nums of size n consisting of non-negative integers. You need to apply n - 1 operations to this array where, in the ith operation (0-indexed), you will apply the following on the ith element of nums: If nums[i] == nums[i + 1], then multiply nums[i] by 2 and set nums[i + 1] to 0. Otherwise, you skip this operation. After performing all the operations, shift all the 0’s to the end of the array. For example, the array [1,0,2,0,0,1] after shifting all its 0’s to the end, is [1,2,1,0,0,0]. Return the resulting array. Note that the operations are applied sequentially, not all at once. Example 1: ...

1323. Maximum 69 Number Hardness: \(\color{green}\textsf{Easy}\) Ralated Topics: Math、Greedy 一、題目 You are given a positive integer num consisting only of digits 6 and 9. Return the maximum number you can get by changing at most one digit (6 becomes 9, and 9 becomes 6). Example 1: Input: num = 9669 Output: 9969 Explanation: Changing the first digit results in 6669. Changing the second digit results in 9969. Changing the third digit results in 9699. Changing the fourth digit results in 9666. The maximum number is 9969. Example 2: ...

79. Word Search Hardness: \(\color{orange}\textsf{Medium}\) Ralated Topics: Array、Backtracking、Matrix 一、題目 Given an m x n grid of characters board and a string word, return true if word exists in the grid. The word can be constructed from letters of sequentially adjacent cells, where adjacent cells are horizontally or vertically neighboring. The same letter cell may not be used more than once. Example 1: Input: board = [[“A”,“B”,“C”,“E”],[“S”,“F”,“C”,“S”],[“A”,“D”,“E”,“E”]], word = “ABCCED” Output: true Example 2: ...

212. Word Search II Hardness: \(\color{red}\textsf{Hard}\) Ralated Topics: Array、String、Backtracking、Trie、Matrix 一、題目 Given an m x n board of characters and a list of strings words, return all words on the board. Each word must be constructed from letters of sequentially adjacent cells, where adjacent cells are horizontally or vertically neighboring. The same letter cell may not be used more than once in a word. Example 1: Input: board = [[“o”,“a”,“a”,“n”],[“e”,“t”,“a”,“e”],[“i”,“h”,“k”,“r”],[“i”,“f”,“l”,“v”]], words = [“oath”,“pea”,“eat”,“rain”] Output: [“eat”,“oath”] Example 2: ...

2131. Longest Palindrome by Concatenating Two Letter Words Hardness: \(\color{orange}\textsf{Medium}\) Ralated Topics: Array、Hash Table、String、Greedy、Counting 一、題目 You are given an array of strings words. Each element of words consists of two lowercase English letters. Create the longest possible palindrome by selecting some elements from words and concatenating them in any order. Each element can be selected at most once. Return the length of the longest palindrome that you can create. If it is impossible to create any palindrome, return 0. ...

433. Minimum Genetic Mutation Hardness: \(\color{orange}\textsf{Medium}\) Ralated Topics: Hash Table、String、Breadth-First Search 一、題目 A gene string can be represented by an 8-character long string, with choices from A, C, G, and T. Suppose we need to investigate a mutation from a gene string start to a gene string end where one mutation is defined as one single character changed in the gene string. For example, "AACCGGTT" --> "AACCGGTA" is one mutation. There is also a gene bank bank that records all the valid gene mutations. A gene must be in bank to make it a valid gene string. Given the two gene strings start and end and the gene bank bank, return the minimum number of mutations needed to mutate from start to end. If there is no such a mutation, return -1. Note that the starting point is assumed to be valid, so it might not be included in the bank. Example 1: ...

20. Valid Parentheses Hardness: \(\color{green}\textsf{Easy}\) Ralated Topics: String、Stack 一、題目 Given a string s containing just the characters (, ), {, }, [ and ], determine if the input string is valid. An input string is valid if: Open brackets must be closed by the same type of brackets. Open brackets must be closed in the correct order. Every close bracket has a corresponding open bracket of the same type. Example 1: ...

1706. Where Will the Ball Fall Hardness: \(\color{orange}\textsf{Medium}\) Ralated Topics: Array、Dynamic Programming、Depth-First Search、Matrix、Simulation 一、題目 You have a 2-D grid of size m x n representing a box, and you have n balls. The box is open on the top and bottom sides. Each cell in the box has a diagonal board spanning two corners of the cell that can redirect a ball to the right or to the left. A board that redirects the ball to the right spans the top-left corner to the bottom-right corner and is represented in the grid as 1. A board that redirects the ball to the left spans the top-right corner to the bottom-left corner and is represented in the grid as -1. We drop one ball at the top of each column of the box. Each ball can get stuck in the box or fall out of the bottom. A ball get stuck if it hits a “V” shaped pattern between two boards or if a board redirects the ball into either wall of the box. Return an array answer of size n where answer[i] is the column that the ball falls out of at the bottom after dropping the ball from the ith column at the top, or -1 if the ball gets stuck in the box. Example 1: ...