Observations 对一个长为 $2N$ 的序列重复下述操作:取走两个相邻且不同的元素.最后能把序列取空的充要条件是序列中不存在出现超过 $N$ 次的元素. 证明:必要性,取 $N$ 次最多能取走 $N$ 个同样的元素,因此同样的元素不能超过 $N$ 个. 充分性可以用归纳法证明.对于元素 A,只要序列中不全是 A,一定能取走一个 A.我们只要证明当序列中有 $N$ 个 A 和 $N$ 个 B 时一定存在相邻的 A 和 B,这是显然的. 转化 题解 其他解法 https://www.cnb…

图中黄色部分为(A-B)U(B-A)的实际意义,用结构数组做静态链表来实现该表达式 大致流程是先建立A链表,接着将挨个输入的B中元素在A链表中遍历.如果没找到,就加到A链表结尾下标为endpointer的位置之后.如果找到了,删除该节点(回收到备用链表中). 需要注意的是: 每次拿着B中元素遍历A链表时,遍历到endpointer就停了.因为endpointer之后的都是B中元素,排除B中有相同元素的可能性,只用与A中元素(即endpointer之前的比较) 代码中,B中元素的插入方式,是在en…

设 $A,B$ 分别是 $3\times 2$ 和 $2\times 3$ 实矩阵. 若 $\dps{AB=\sex{\ba{ccc}  8&0&-4\\  -\frac{3}{2}&9&-6\\  -2&0&1  \ea}}$, 求 $BA$. 解答: 由  $$\bex  AB\rra\sex{\ba{ccc}  1&0&-\frac{1}{2}\\\  0&1&-\frac{3}{4}\\  0&0&0…

其实更为直观的理解是:AB与BA具有相同的对角线元素,因此tr(AB)=tr(BA)必然成立 ref:https://blog.csdn.net/silence1214/article/details/8632357…

Description 一个长度为 n 的字符串是好的当且仅当它由 'A', 'B', 'C' 组成,且可以通过若干次删除除了"AB"和"BA"的连续子串变为空串. 问有多少个长度为 n 的好串,对 998244353 取模. \(n\le 10 ^ 7\) , 保证 n 为偶数. Solution 本题的关键在于转化题意,即找到一个更加简洁抽象的等价条件方便计数. 连续删除两个字符后发现每一个 A 和 B 的奇偶性没有改变. 这说明了奇数位置的 A 一定不能和偶数…

目录 @description@ @solution@ @accepted code@ @detail@ @description@ 给定偶数 N,求由 'A', 'B', 'C' 三种字符组成的字符串 S,有多少满足如下的条件: 每次可以选择 S 中的两个相邻字符(不能选择 "AB" 与 "BA"),删除它们.最后可以将 S 删成空串. 比如:"ABBC" -> "AC" -> "".所以 &…

正题 题目链接:https://www.luogu.com.cn/problem/AT5661 题目大意 一个包含\(A,B,C\)的序列,每次可以选择相邻的两个除了\(AB\)和\(BA\)的删去. 求有多少个长度为\(N\)的序列可以删完. \(1\leq N\leq 10^7\) 解题思路 因为每次是删除一个奇数位置和一个偶数位置,如果我们把所有偶数位置的取反,那么就变成了不能删除\(AA\)和\(BB\). 然后如果在边上\(A\)一定可以删(除非到边界),也就是\(A\)的数量不能超过…

传送门 好妙的题啊 首先容易想到简单容斥,统计合法方案数可以考虑总方案数减去不合法方案数 那么先考虑如何判断一个串是否合法,但是直接判断好像很不好搞 这时候就需要一些 $magic$ 了,把所有位置下标为奇数的字符 $\text{A}$ 换成 $\text{B}$ ,$\text{B}$ 换成 $\text{A}$ 然后发现对于转化后的串,原本的限制变成了不能删除 $AA$ 和 $BB$ ,考虑到原串和新串是一一对应的 所以如果能算出合法新串的数量那么即为答案 然后容易发现,新串合法的充分必要条…

A. Two Substrings time limit per test 2 seconds memory limit per test 256 megabytes input standard input output standard output You are given string s. Your task is to determine if the given string s contains two non-overlapping substrings "AB"…

The vast power system is the most complicated man-made system and the greatest engineering innovation in the 20th century. The following diagram shows a typical 14 bus power system. In real world, the power system may contains hundreds of buses and t…

Task 题目连接: https://icpcarchive.ecs.baylor.edu/index.php?option=com_onlinejudge&Itemid=8&page=show_problem&problem=2886 Description In most recipes, certain tasks have to be done before others. For each task, if we are given a list of other tas…

设 $A,B$ 是 $n$ 阶实对称矩阵. 试证: $\tr((AB)^2)\leq \tr(A^2B^2)$. 又问: 等号何时成立? 证明:  由  $$\bex  \sum_i \sez{\sum_j a_{ij}b_{ji}}=\sum_j\sez{\sum_i b_{ji}a_{ij}}  \eex$$  知  $$\bee\label{130912:1}  \tr(AB)=\tr(BA).  \eee$$  对 $A,B\in M_n(\bbR)$, 定义  $$\bex  \sef…

Going from u to v or from v to u? Time Limit: 2000MS   Memory Limit: 65536K Total Submissions: 17089   Accepted: 4590 Description In order to make their sons brave, Jiajia and Wind take them to a big cave. The cave has n rooms, and one-way corridors…

Detecting diabetic retinopathy in eye images The past almost four months I have been competing in a Kaggle competition about diabetic retinopathy grading based on high-resolution eye images. In this post I try to reconstruct my progression through th…

A. Two Substrings Time Limit: 20 Sec Memory Limit: 256 MB 题目连接 http://codeforces.com/contest/550/problem/A Description You are given string s. Your task is to determine if the given string s contains two non-overlapping substrings "AB" and "…

Two Substrings time limit per test 2 seconds memory limit per test 256 megabytes input standard input output standard output You are given string s. Your task is to determine if the given string s contains two non-overlapping substrings "AB" and…

A. Two Substrings You are given string s. Your task is to determine if the given string s contains two non-overlapping substrings "AB" and "BA" (the substrings can go in any order). Input The only line of input contains a string s of l…

Mr. Frog's Problem Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 65536/65536 K (Java/Others)Total Submission(s): 312    Accepted Submission(s): 219 Problem Description One day, you, a clever boy, feel bored in your math class, and then fall…

If you hide some digits in an integer equation, you create a digit puzzle. The figure below shows two validdigit puzzles. Hidden digits are represented by squares, and other digits are shown. The numbers involved inthis problem are all positive integ…

2780: Poi2006 Palindromes Time Limit: 10 Sec  Memory Limit: 512 MBSubmit: 15  Solved: 5[Submit][Status][Web Board] Description A word is called a palindrome if we read from right to left is as same as we read from left to right. For example, "dad&quo…

Windows下没有比较好的Markdown编辑器 我就自己写一个 csdn的Markdown很好,就是我需要截图保存有麻烦 需要把我的截图保存在本地,然后上传 这个过程比较麻烦 csdn的图没法外链 我想把自己的博客放到github,发现都没有图片 我自己写了的,可以把截图保存为图片,放到用户位置 然后插入 拖入图片也插入 界面有编辑和设置 编辑由TopAppBar,TextBox作为输入和TextBlock显示 拖入…

threading python程序默认是单线程的,也就是说在前一句语句执行完之前后面的语句不能继续执行(不知道我理解得对不对) 先感受一下线程,一般情况下: def testa(): sleep(1) print "a" def testb(): sleep(1) print "b" testa() testb() #先隔出一秒打印出a,再过一秒打出b 但是如果用了threading的话: ta = threading.Thread(target=testa) t…

关键词:LockDep.spinlock.mutex. lockdep是内核提供协助发现死锁问题的功能. 本文首先介绍何为lockdep,然后如何在内核使能lockdep,并简单分析内核lockdep相关代码. 最后构造不同死锁用例,并分析如何根据lockdep输出发现问题根源. 1. Lockdep介绍 死锁是指两个或多个进程因争夺资源而造成的互相等待的现象. 常见的死锁有如下两种: 递归死锁:中断等延迟操作中使用了锁,和外面的锁构成了递归死锁. AB-BA死锁:多个锁因处理不当而引发死锁,多…

Finding Palindromes Time Limit: 10000MS   Memory Limit: 262144K Total Submissions:4710   Accepted: 879 Case Time Limit: 2000MS Description A word is called a palindrome if we read from right to left is as same as we read from left to right. For examp…

Windows下没有比較好的Markdown编辑器 我就自己写一个 csdn的Markdown非常好,就是我须要截图保存有麻烦 须要把我的截图保存在本地,然后上传 这个过程比較麻烦 csdn的图没法外链 我想把自己的博客放到github.发现都没有图片 我自己写了的,能够把截图保存为图片,放到用户位置 然后插入 拖入图片也插入 界面有编辑和设置 编辑由TopAppBar,TextBox作为输入和TextBlock显示 拖…

[题目链接]click here~~  [题目大意]:  You are given string s. Your task is to determine if the given string s contains two non-overlapping substrings "AB" and "BA" (the substrings can go in any order).  Input  The only line of input contains a…

A. Two Substrings time limit per test 2 seconds memory limit per test 256 megabytes input standard input output standard output You are given string s. Your task is to determine if the given string s contains two non-overlapping substrings "AB"…

Finding Palindromes http://poj.org/problem?id=3376 Time Limit: 10000MS   Memory Limit: 262144K       Case Time Limit: 2000MS Description A word is called a palindrome if we read from right to left is as same as we read from left to right. For example…

You've got string s, consisting of small English letters. Some of the English letters are good, the rest are bad. A substring s[l...r] (1 ≤ l ≤ r ≤ |s|) of string s  =  s1s2...s|s| (where|s| is the length of string s) is string  slsl + 1...sr. The su…

传送门 D. Good Substrings time limit per test 2 seconds memory limit per test 512 megabytes input standard input output standard output You've got string s, consisting of small English letters. Some of the English letters are good, the rest are bad. A s…