Hi, I'm Louislan ! 👋🏼

题目地址 https://leetcode.com/problems/clone-graph/ 题目描述 Given a reference of a node in a connected undirected graph. Return a deep copy (clone) of the graph. Each node in the graph contains a val (int) and a list (List[Node]) of its neighbors. class Node { public int val; public List<Node> neighbors; } Test case format: For simplicity sake, each node's value is the same as the node's index (1-indexed). For example, the first node with val = 1, the second node with val = 2, and so on. The gra....

题目地址 https://leetcode.com/problems/palindrome-partitioning-ii/ 题目描述 Given a string s , partition s such that every substring of the partition is a palindrome. Return the minimum cuts needed for a palindrome partitioning of s. Example: Input: "aab" Output: 1 Explanation: The palindrome partitioning ["aa","b"] could be produced using 1 cut. 思路 这道题是让找到把原字符串拆分成回文串的最小切割数，如果我们首先考虑用 brute force 来做的话就会十分的复杂，因为我们不但要判断子串是否是回文串，而且还要找出最小切割数，情况会非常的多，不好做。所以对于这种玩字符串且是求极值的题，就要祭出旷古神器动态规划 Dynamic Programming 了，秒....

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”....