LouisLan的学习简记 👋🏼

题目地址 https://leetcode.com/problems/palindrome-partitioning/ 题目描述 Given a string s , partition s such that every substring of the partition is a palindrome. Return all possible palindrome partitioning of s. Example: Input: "aab" Output: [ ["aa","b"], ["a","a","b"] ] 思路 这又是一道需要用 DFS 来解的题目，既然题目要求找到所有可能拆分成回文数的情况，那么肯定是所有的情况都要遍历到，对于每一个子字符串都要分别判断一次是不是回文数，那么肯定有一个判断回文数的子函数，还需要一个 DFS 函数用来递归，再加上原本的这个函数，总共需要三个函数来求解。我们将已经检测好的回文子串放到字符串数组 out 中，当 s 遍历完了之后，将 out 加入结果 res 中。那么在递归函数中我们必须要知道当前遍历到的位置，用变量 start 来表示....

\color{green}{Do} \color{green}{you} \color{green}{believe} \color{green}{in} \color{green}{god?} \color{red}{Yes.} \color{green}{How} \color{green}{can} \color{green}{you?} \color{red}{I} \color{red}{can't} \color{red}{believe} \color{red}{in} \color{red}{people.} \color{red}{I} \color{red}{have} \color{red}{to} \color{red}{believe} \color{red}{in} \color{red}{something,} \color{red}{or} \color{red}{I'd} \color{red}{fall.} 我是谁 😄 97后，2019年 计算机科学与技术专业本科 毕业，略知前端和增删改查的技术小白。现入职某运营商，暂时脱离了技术，向往....

题目地址 https://leetcode.com/problems/surrounded-regions/ 题目描述 Given a 2D board containing 'X' and 'O'(the letter O), capture all regions surrounded by 'X'. A region is captured by flipping all 'O's into 'X's in that surrounded region. Example: X X X X X O O X X X O X X O X X After running your function, the board should be: X X X X X X X X X X X X X O X X Explanation: Surrounded regions shouldn’t be on the border, which means that any 'O' on the border of the board are not flipped to 'X'. Any 'O....

题目地址 https://leetcode.com/problems/sum-root-to-leaf-numbers/ 题目描述 Given a binary tree containing digits from 0-9 only, each root-to-leaf path could represent a number. An example is the root-to-leaf path 1->2->3 which represents the number 123. Find the total sum of all root-to-leaf numbers. Note: A leaf is a node with no children. Example: Input: [1,2,3] 1 / \ 2 3 Output: 25 Explanation: The root-to-leaf path 1->2 represents the number 12. The root-to-leaf path 1->3 represents the n....

题目地址 https://leetcode.com/problems/longest-consecutive-sequence/ 题目描述 Given an unsorted array of integers, find the length of the longest consecutive elements sequence. Your algorithm should run in O( n ) complexity. Example: Input: [100, 4, 200, 1, 3, 2] Output: 4 Explanation: The longest consecutive elements sequence is [1, 2, 3, 4]. Therefore its length is 4. 思路 这道题要求求最长连续序列，并给定了 O(n)复杂度限制，我们的思路是，使用一个集合 HashSet 存入所有的数字，然后遍历数组中的每个数字，如果其在集合中存在，那么将其移除，然后分别用两个变量 pre 和 next 算出其前一个数跟后一个数，然后在集合中循环查....

题目地址 https://leetcode.com/problems/word-ladder/ 题目描述 Given two words ( beginWord and endWord ), and a dictionary's word list, find the length of shortest transformation sequence from beginWord to endWord , such that: Only one letter can be changed at a time. Each transformed word must exist in the word list. Note that beginWord is not a transformed word. Note: Return 0 if there is no such transformation sequence. All words have the same length. All words contain only lowercase alphabetic char....

题目地址 https://leetcode.com/problems/word-ladder-ii/ 题目描述 Given two words ( beginWord and endWord ), and a dictionary's word list, find all shortest transformation sequence(s) from beginWord to endWord , such that: Only one letter can be changed at a time Each transformed word must exist in the word list. Note that beginWord is not a transformed word. Note: Return an empty list if there is no such transformation sequence. All words have the same length. All words contain only lowercase alphabet....

题目地址 https://leetcode.com/problems/valid-palindrome/ 题目描述 Given a string, determine if it is a palindrome, considering only alphanumeric characters and ignoring cases. For example, "A man, a plan, a canal: Panama" is a palindrome. "race a car" is not a palindrome. Note: Have you consider that the string might be empty? This is a good question to ask during an interview. For the purpose of this problem, we define empty string as valid palindrome. 思路 验证回文字符串是比较常见的问题，所谓回文，就是一个正读和反读都一样的字符串，比如“level”....

题目地址 https://leetcode.com/problems/binary-tree-maximum-path-sum/ 题目描述 Given a non-empty binary tree, find the maximum path sum. For this problem, a path is defined as any sequence of nodes from some starting node to any node in the tree along the parent-child connections. The path must contain at least one node and does not need to go through the root. Example 1: Input: [1,2,3] 1 / \ 2 3 Output: 6 Example 2: Input: [-10,9,20,null,null,15,7] -10 / \ 9 20 / \ 15 7 Output: 42 思路 这道求二叉树的最大路径和是一道蛮有....

题目地址 https://leetcode.com/problems/best-time-to-buy-and-sell-stock-iii/ 题目描述 Say you have an array for which the i th element is the price of a given stock on day i. Design an algorithm to find the maximum profit. You may complete at most two transactions. Note: You may not engage in multiple transactions at the same time (i.e., you must sell the stock before you buy again). Example 1: Input: [3,3,5,0,0,3,1,4] Output: 6 Explanation: Buy on day 4 (price = 0) and sell on day 6 (price = 3), profit ....