这道题是这种,给主人公一堆事件的成功概率,他仅仅想恰好成功一件. 于是,问题来了,他要选择哪些事件去做,才干使他的想法实现的概率最大. 我的第一个想法是枚举,枚举的话我想到用dfs,但是认为太麻烦. 于是想是不是有什么规律,于是推导了一下,推了一个出来,写成代码提交之后发现是错的. 最后就没办法了,剩下的时间不够写dfs,于是就放弃了. 今天看thnkndblv的代码,代码非常短,于是就想肯定是有什么数学规律,于是看了一下, 果然如此. 是这种,还是枚举,当然是有技巧的,看我娓娓道来. 枚举的话…

题目链接: B. Andrey and Problem time limit per test 2 seconds memory limit per test 256 megabytes input standard input output standard output Andrey needs one more problem to conduct a programming contest. He has n friends who are always willing to help.…

http://codeforces.com/problemset/problem/442/B (题目链接) 题意 n个人,每个人有p[i]的概率出一道题.问如何选择其中s个人使得这些人正好只出1道题的概率最大. Solution 很显然的概率dp,过了样例即可AC..话说我为什么要刷B题→_→ 代码 // codeforces442B #include<algorithm> #include<iostream> #include<cstdlib> #include<…

[链接] 我是链接,点我呀:) [题意] n个朋友 第i个朋友帮你的概率是pi 现在问你恰好有一个朋友帮你的概率最大是多少 前提是你可以选择只问其中的某些朋友不用全问. [题解] 主要思路是逆向思维,转换成一个一个地加上去 然后看看概率的改变值在何时为正数,显然只有为正数的时候才能加 然后概率大的和概率小的,哪一个加上去会比较优一点,也比较一下. 但是因为加上去之后S也会变化,所以只知道概率大的加上去比较优还不够. 可以再看看下面那个反证法. 它指出为何一定是选择末尾最大的若干个(也即优先选择p…

B. Andrey and Problem time limit per test 2 seconds memory limit per test 256 megabytes input standard input output standard output Andrey needs one more problem to conduct a programming contest. He has n friends who are always willing to help. He ca…

题目链接:Codeforces 442B Andrey and Problem 题目大意:Andrey有一个问题,想要朋友们为自己出一道题,如今他有n个朋友.每一个朋友想出题目的概率为pi,可是他能够同一时候向多个人寻求帮助.只是他仅仅能要一道题,也就是假设他向两个人寻求帮助,假设两个人都成功出题,也是不能够的. 解题思路:贪心,从概率最大的人開始考虑.假设询问他使得概率变大,则要询问. #include <cstdio> #include <cstring> #include &…

B. Andrey and Problem time limit per test 2 seconds memory limit per test 256 megabytes input standard input output standard output Andrey needs one more problem to conduct a programming contest. He has n friends who are always willing to help. He ca…

B. Andrey and Problem time limit per test 2 seconds memory limit per test 256 megabytes input standard input output standard output Andrey needs one more problem to conduct a programming contest. He has n friends who are always willing to help. He ca…

1. 题目 我的提交 GZS的三角形 发布时间: 2015年9月6日 15:18   最后更新: 2016年6月26日 12:10   时间限制: 1000ms   内存限制: 256M 描述 机智无比的G神今天完成了一天的任务,实在是无聊的紧,拿起一支笔在纸上画起了三角形,边长为1, 2, 3,......... 即使是无聊到这种程度,G神发达的大脑也在不停的思考,从顶部的点到沿着所画出的边到达底边的方案有多少种呢. 结果可能比较大, 结果对1000003取余. 例如,边长为2的情况如下所示:…

关于证明可以参考题解http://codeforces.com/blog/entry/12739 就是将概率从大到小排序然后,然后从大到小计算概率 #include <iostream> #include <vector> #include <string> #include <algorithm> #include <functional> #include <cstdio> using namespace std; int mai…

概率计算:P(某set) =  令:  和   现在考虑: 1.考虑某个集合,再加一个概率为Pi的朋友后能不能使总概率提高. 即: 由公式可知, 如果 S < 1,则delta > 0,则可以加入这个朋友. 2.如果要加一个朋友有两个候选的,其概率分别为Pi,Pj,(设Pi < Pj)那么加哪个会更优呢? Δi - Δj = P·pi·(1 - S) - P·pj·(1 - S) = P·(1 - S)·(pi - pj) > 0.  如果 S < 1 那么 pi > …

time limit per test 2 seconds memory limit per test 256 megabytes input standard input output standard output Andrey needs one more problem to conduct a programming contest. He has n friends who are always willing to help. He can ask some of them to…

Problem - C - Codeforces 看清题目要求, 最重要部分在第二段. 大佬最后给出的代码果然简单, 思路简单化, 未必非要把答案在一个大括号里全部完成, 两个指针同时跑,中间加了一堆判断处理, 反而不如返璞归真, 简单清晰为后面改代码也省了很多力气 AC代码 #include <iostream> #include <algorithm> using namespace std; typedef long long LL; const int N = 2e5+10…

题目链接:http://codeforces.com/problemset/problem/442/B 题目大意:有n个人,第i个人出一道题的概率是pi,现在选出一个子集,使得这些人恰好出一个题的概率最大.问最大概率. 可以仿照背包问题来做,即每个人可问可不问. f[i][j]代表从前i个人里问j个人所获得1个题的最大概率. f[i][j] = max{ f[i-1][j], f[i-1][j-1]*(1-p[i])+z[i-1][j-1]*p[i] }; z[i][j]为从前i个人里问j个人所…

Another Rock-Paper-Scissors Problem 题目连接: http://codeforces.com/gym/100015/attachments Description Sonny uses a very peculiar pattern when it comes to playing rock-paper-scissors. He likes to vary his moves so that his opponent can't beat him with hi…

当在Codeforces上做题的时,有时会无意撇到右侧的Problem tags边栏,但是原本并不希望能够看到它. 能否把它屏蔽了呢?答案是显然的,我们只需要加一段很短的CSS即可. span.tag-box{ display: none; } 这样,当这段CSS生效时,标签将会变成如下所示的样子. 这样目的就达到了. 那么,如何将CSS应用到浏览器中使其生效呢?对于不同的浏览器有不同的方法.下面以主流浏览器为例. 对于Safari,将上述代码另存为.css文件,然后在偏好设置->高级->样式…

http://codeforces.com/contest/426/problem/B 对称标题的意思大概是.应当指出的,当线数为奇数时,答案是线路本身的数 #include<iostream> #include<cstdio> #include<cstring> #include<algorithm> #define maxn 1005 using namespace std; char a[maxn][maxn]; int ans; void solve…

ZOJ Problem Set - 3593 http://acm.zju.edu.cn/onlinejudge/showProblem.do?problemCode=3593 One Person Game Time Limit: 2 Seconds      Memory Limit: 65536 KB There is an interesting and simple one person game. Suppose there is a number axis under your f…

题目链接:http://codeforces.com/problemset/problem/803/G 大致就是线段树动态开节点. 然后考虑到如果一个点还没有出现过,那么这个点显然未被修改,就将这个点所代表的区间定位到原序列中,利用ST表查一下区间最小值就可以了. 定位: llg minn(llg l,llg r) { >=n) return mt; l%=n;if(!l) l=n; r%=n;if(!r) r=n; ,r)); else return gw(l,r); } 其中${gw(l,r…

题目传送门 传送门I 传送门II 传送门III 题目大意 给定一个网络.网络分为$A$,$B$两个部分,每边各有$n$个点.对于$A_{i} \ (1\leqslant i < n)$会向$A_{i + 1}$连一条容量为$x_{i}$的有向边,对于$B_{i} \ (1\leqslant i < n)$会向$B_{i + 1}$连一条容量为$y_{i}$的有向边.$A$和$B$之间有$m$条边,起点为$A_{u_{i}}$,终点为$B_{v_{i}}$,容量为$w_{i}$的有向边.要求支持…

Adieu l'ami. Koyomi is helping Oshino, an acquaintance of his, to take care of an open space around the abandoned Eikou Cram School building, Oshino's makeshift residence. The space is represented by a rectangular grid of n × m cells, arranged into n…

— This is not playing but duty as allies of justice, Nii-chan! — Not allies but justice itself, Onii-chan! With hands joined, go everywhere at a speed faster than our thoughts! This time, the Fire Sisters — Karen and Tsukihi — is heading for somewher…

Even if the world is full of counterfeits, I still regard it as wonderful. Pile up herbs and incense, and arise again from the flames and ashes of its predecessor — as is known to many, the phoenix does it like this. The phoenix has a rather long lif…

Rock... Paper! After Karen have found the deterministic winning (losing?) strategy for rock-paper-scissors, her brother, Koyomi, comes up with a new game as a substitute. The game works as follows. A positive integer n is decided first. Both Koyomi a…

Palindromic characteristics of string s with length |s| is a sequence of |s| integers, where k-th number is the total number of non-empty substrings of s which are k-palindromes. A string is 1-palindrome if and only if it reads the same backward as f…

The Cartesian coordinate system is set in the sky. There you can see n stars, the i-th has coordinates (xi, yi), a maximum brightness c, equal for all stars, and an initial brightness si (0 ≤ si ≤ c). Over time the stars twinkle. At moment 0 the i-th…

Two boys decided to compete in text typing on the site "Key races". During the competition, they have to type a text consisting of s characters. The first participant types one character in v1 milliseconds and has ping t1 milliseconds. The secon…

Misha and Grisha are funny boys, so they like to use new underground. The underground has n stations connected with n - 1 routes so that each route connects two stations, and it is possible to reach every station from any other. The boys decided to h…

n people are standing on a coordinate axis in points with positive integer coordinates strictly less than 106. For each person we know in which direction (left or right) he is facing, and his maximum speed. You can put a bomb in some point with non-n…

It's hard times now. Today Petya needs to score 100 points on Informatics exam. The tasks seem easy to Petya, but he thinks he lacks time to finish them all, so he asks you to help with one.. There is a glob pattern in the statements (a string consis…