题目：Given an integer n, generate a square matrix filled with elements from 1 to n2 in spiral order.For example,
Given n = 3,You should return the following matrix:[[ 1, 2, 3 ],[ 8, 9, 4 ],[ 7, 6, 5 ]
]题意：给定一个整数 n,生成一个正方形矩阵。矩阵中包含着从1到n2 这些元素，并且以螺旋顺序排列。比如，给定n = 3,你应该返回如下的矩阵：[[ 1, 2, 3 ],[ 8, 9, 4 ],[ 7, 6, 5 ]
]算法分析：和题目《Spiral Matri...
题目：Given a 2D board containing ‘X‘ and ‘O‘,capture all regions surrounded by ‘X‘.A region is captured by flipping all ‘O‘s into ‘X‘sin that surrounded region.For 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题意：给定一个2维平面包含‘X‘ 和 ‘O‘,填充所有的被‘X‘包围的区域.比如，X X X X
X O O X
X X O X
X O X X...
5449. 检查数组对是否可以被 k 整除 给你一个整数数组 arr 和一个整数 k ，其中数组长度是偶数，值为 n 。现在需要把数组恰好分成 n / 2 对，以使每对数字的和都能够被 k 整除。如果存在这样的分法，请返回 True ；否则，返回 False 。 示例 1：输入：arr = [1,2,3,4,5,10,6,7,8,9], k = 5
输出：true
解释：划分后的数字对为 (1,9),(2,8),(3,7),(4,6) 以及 (5,10) 。
示例 2：输入：arr = [1,2,3,4,5,6], k = 7
输出：true
解释：...
题目：匹配正则表达式题目难度：hard题目内容：Implement regular expression matching with support for ‘.‘ and ‘*‘.‘.‘ Matches any single character.
‘*‘ Matches zero or more of the preceding element.The matching should cover the entire input string (not partial).The function prototype should be:
bool isMatch(const char *s, const char *p)翻译：" . "匹配任何一个字符。" * "匹配零个或更多的前面...
【034-Search for a Range（搜索一个范围）】【LeetCode-面试算法经典-Java实现】【所有题目目录索引】原题 Given a sorted array of integers, 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]. For example, Given [5, 7, 7, 8, 8, 10] and target value 8, return [3, ...
题目：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 timeEach 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.Al...
题目链接：majority-element/*** Given an array of size n, find the majority element. The majority element is the element that appears more than ? n/2 ? times.You may assume that the array is non-empty and the majority element always exist in the array.**/
public class MajorityElement {// 40 / 40 test cases passed.
// Status: Accepted
// Runtime: 253 ms
// Submitted: 1 minute ago//时间复杂度为 O(n),...
【225-Implement Stack using Queues（用队列实现栈操作）】【LeetCode-面试算法经典-Java实现】【所有题目目录索引】代码下载【https://github.com/Wang-Jun-Chao】原题 Implement the following operations of a stack using queues. push(x) – Push element x onto stack. pop() – Removes the element on top of the stack. top() – Get the top element. empty() – Return whether the stack is empty. Notes: You mus...
参考：https://www.bilibili.com/video/BV14f4y1C7hg
宝藏up主！1.时间复杂度O(1)O(n)复杂度看最高的O(n2)
如果只是两个并列的for循环，时间复杂度还是O（n），100个并列的for循环，也是O(n)这里有继承，两个循环分摊一个任务O(logn)二分搜索O(nlogn)排序优化的方法:从低-级的复杂度寻找灵感O(n)->O(logn)使用二分搜索O(nlogn) -> O(n)遇到需要排序的题，想想能否通过数组,set, map,heap解O(n2)-> O(nlogn)遇到嵌套循环，想想能不能...
Bulb SwitcherThere are n bulbs that are initially off. You first turn on all the bulbs. Then, you turn off every second bulb. On the third round, you toggle every third bulb (turning on if it‘s off or turning off if it‘s on). For the nth round, you only toggle the last bulb. Find how many bulbs are on after n rounds.Example:Given n = 3.
At first, the three bulbs are [off, off, off].
After first...
1. 具体题目给定一个字符串，验证它是否是回文串，只考虑字母和数字字符，可以忽略字母的大小写。说明：本题中，我们将空字符串定义为有效的回文串。示例 1: 输入: "A man, a plan, a canal: Panama" 输出: true示例 2: 输入: "race a car" 输出: false2. 思路分析对于给定的字符串，其中可能包括有无效字符，所以需要先将原字符串中的无效字符去掉（用正则表达式判断），得到新字符串后用双指针比较首尾字符是否相等。...
题目：
Given a sorted linked list, delete all duplicates such that each element appear only once.For example,
Given 1->1->2, return 1->2.
Given 1->1->2->3->3, return 1->2->3.
题解：这道题是经典的双指针问题，用两个指针一前一后指向链表。如果两个指针指向的值相等，那么就让第二个指针一直往后挪，挪到与第一个指针不同为止。然后让第一个指针的next指向第二个指针，两个指针同时往后挪，进行下面的操作。需要注意...
【101-Symmetric Tree（对称树）】【LeetCode-面试算法经典-Java实现】【所有题目目录索引】原题 Given a binary tree, check whether it is a mirror of itself (ie, symmetric around its center). For example, this binary tree is symmetric: 1/ 2 2/ \ / 3 4 4 3 But the following is not: 1/ 2 2\ 3 3 Note: Bonus points if you could solve it both recursively and iteratively.题目大意...
【070-Set Matrix Zeroes（矩阵置零）】【LeetCode-面试算法经典-Java实现】【所有题目目录索引】原题 Given a m x n matrix, if an element is 0, set its entire row and column to 0. Do it in place. 题目大意 给定一个m*n的矩阵，如果某个位置是0。将对应的行和列设置为0。 解题思路 先对矩阵进行扫描，标记要进行置0的行和列，对要进行置0的行在第0列上进行标记，对置0的列在第0行上进行标标记。同时还要两变量记录...
https://leetcode.com/problems/longest-valid-parentheses/Longest Valid ParenthesesGiven a string containing just the characters ‘(‘ and ‘)‘, find the length of the longest valid (well-formed) parentheses substring.For "(()", the longest valid parentheses substring is "()", which has length = 2.Another example is ")()())", where the longest valid parentheses substring is "()()", which has length...
