LouisLan的学习简记 👋🏼

题目地址 https://leetcode.com/problems/first-missing-positive/ 题目描述 Given an unsorted integer array, find the smallest missing positive integer. Example 1: Input: [1,2,0] Output: 3 Example 2: Input: [3,4,-1,1] Output: 2 Example 3: Input: [7,8,9,11,12] Output: 1 Note: Your algorithm should run in O ( n ) time and uses constant extra space. 思路 这道题让我们找缺失的首个正数，由于限定了 O(n) 的时间，所以一般的排序方法都不能用，最开始博主没有看到还限制了空间复杂度，所以想到了用 HashSet 来解，这个思路很简单，把所有的数都存入 HashSet 中，然后循环从 1 开始递增找数字，哪个数字找不到就返回哪个数字，如果一直找到了最大的数字（这里是 n....

? 我在做什么？ 果然，人都是有惰性的啊，这才坚持几天我就不想继续做下去了，也不是说不想做下去，就今天感觉没有那个心情继续。。 感觉潜意识里把他当成了一个任务，而不是自己想做的一件事情。 果然还是懒惰在犯罪。 少坚持一天，离放弃还有多远呢。 今天的任务不完成，我就..

题目地址 https://leetcode.com/problems/combination-sum-ii/ 题目描述 Given a collection of candidate numbers (candidates) and a target number (target), find all unique combinations in candidates where the candidate numbers sums to target. Each number in candidates may only be used once in the combination. Note: All numbers (including target) will be positive integers. The solution set must not contain duplicate combinations. Example 1: Input: candidates = [10,1,2,7,6,1,5], target = 8, A solution set is....

题目地址 https://leetcode.com/problems/combination-sum 题目描述 Given a set of candidate numbers (candidates) (without duplicates) and a target number (target), find all unique combinations in candidates where the candidate numbers sums to target. The same repeated number may be chosen from candidates unlimited number of times. Note: All numbers (including target) will be positive integers. The solution set must not contain duplicate combinations. Example 1: Input: candidates = [2,3,6,7], target = 7, ....

题目地址 https://leetcode.com/problems/count-and-say 题目描述 The count-and-say sequence is the sequence of integers with the first five terms as following: 1. 1 2. 11 3. 21 4. 1211 5. 111221 1 is read off as "one 1" or 11. 11 is read off as "two 1s" or 21. 21 is read off as "one 2, then one 1" or 1211. Given an integer n where 1 ≤ n ≤ 30, generate the n th term of the count-and-say sequence. Note: Each term of the sequence of integers will be represented as a string. Example 1: Input: 1 Output: "1" E....

题目地址 https://leetcode.com/problems/sudoku-solver 题目描述 Write a program to solve a Sudoku puzzle by filling the empty cells. A sudoku solution must satisfy all of the following rules: Each of the digits 1-9 must occur exactly once in each row. Each of the digits 1-9 must occur exactly once in each column. Each of the the digits 1-9 must occur exactly once in each of the 9 3x3 sub-boxes of the grid. Empty cells are indicated by the character '.'. A sudoku puzzle... ...and its solution numbers m....

题目地址 https://leetcode.com/problems/valid-sudoku/ 题目描述 Determine if a 9x9 Sudoku board is valid. Only the filled cells need to be validated according to the following rules: Each row must contain the digits 1-9without repetition. Each column must contain the digits 1-9 without repetition. Each of the 9 3x3 sub-boxes of the grid must contain the digits 1-9 without repetition. A partially filled sudoku which is valid. The Sudoku board could be partially filled, where empty cells are filled with ....

题目地址 https://leetcode.com/problems/search-insert-position/ 题目描述 Given a sorted array and a target value, return the index if the target is found. If not, return the index where it would be if it were inserted in order. You may assume no duplicates in the array. Example 1: Input: [1,3,5,6], 5 Output: 2 Example 2: Input: [1,3,5,6], 2 Output: 1 Example 3: Input: [1,3,5,6], 7 Output: 4 Example 4: Input: [1,3,5,6], 0 Output: 0 思路 这道题基本没有什么难度，实在不理解为啥还是 Medium 难度的，完完全全的应该是 Easy 啊（貌似现在已经改为 Easy 类了），....

题目地址 https://leetcode.com/problems/find-first-and-last-position-of-element-in-sorted-array/ 题目描述 Given an array of integers nums sorted in ascending order, find the starting and ending position of a given target value. Your algorithm's runtime complexity must be in the order of O (log n ). If the target is not found in the array, return [-1, -1]. Example 1: Input: nums = [5,7,7,8,8,10], target = 8 Output: [3,4] Example 2: Input: nums = [5,7,7,8,8,10], target = 6 Output: [-1,-1] 思路 这道题让我们在一个有序整....

题目地址 https://leetcode.com/problems/search-in-rotated-sorted-array/ 题目描述 Suppose an array sorted in ascending order is rotated at some pivot unknown to you beforehand. (i.e., [0,1,2,4,5,6,7] might become [4,5,6,7,0,1,2]). You are given a target value to search. If found in the array return its index, otherwise return -1. You may assume no duplicate exists in the array. Your algorithm's runtime complexity must be in the order of O (log n ). Example 1: Input: nums = [4,5,6,7,0,1,2], target = 0 Outp....