一个合法的三角形的充要条件是a<b+c,其中a为最长的一边,可以考虑找出所有不满足的情况然后用总方案减去不合法的情况. 对于一个给定的总长度tl(一定要分完,因为是枚举tl,不分配的长度已经考虑过了),分成三份,因为可以有两份为零,采用插空法的时候 增加两个假想长度为零的单位,所以方案数是C(tl+2,2), 假设a是增加长度以后最长的一边,r是tl减去给a增加长度之后剩下的长度, 那么不满足的情况的条件就可以写成a+tl-r>=b+c+r,很容易转化为r<=(a-b-c+tl)/2,显…

Pythagorean Triples 题目链接: http://codeforces.com/contest/707/problem/C Description Katya studies in a fifth grade. Recently her class studied right triangles and the Pythagorean theorem. It appeared, that there are triples of positive integers such th…

Codeforces Round #622 (Div. 2) B. Different Rules 题意: 你在参加一个比赛,最终按两场分赛的排名之和排名,每场分赛中不存在名次并列,给出参赛人数 n 和你两场分赛的排名 x, y,问你最终名次最小和最大可能是多少. 思路: 以8人为例: x + y = 2,最小第一名,最大第一名:               1 2 3 4 5 6 7 8 8 7 6 5 4 3 2 1               x + y = 3,最小第一名,最大第二名.…

Problem A Arrays 思路:水一水. #include<bits/stdc++.h> using namespace std; ; int n1,n2,k,m,a[N],b[N]; int main() { scanf("%d%d",&n1,&n2); scanf("%d%d",&k,&m); ;i<=n1;i++) scanf("%d",&a[i]); ;i<=n2;i…

A. Watching a movie time limit per test 1 second memory limit per test 256 megabytes input standard input output standard output You have decided to watch the best moments of some movie. There are two buttons on your player: Watch the current minute…

D. Minimization time limit per test  2 seconds memory limit per test  256 megabytes input  standard input  output  standard output You've got array A, consisting of n integers and a positive integer k. Array A is indexed by integers from 1 to n. You…

题目链接: http://codeforces.com/contest/712/problem/E 题目大意: 一条直线上有n格,在第i格有pi的可能性向右走一格,1-pi的可能性向左走一格,有2中操作:单点修改pi以及询问从L格出发最终从R格离开区间[L,R]的概率. 这题在cf上A的人比较少,本来不打算去做的,然后看了下是概率的题目,比较感兴趣,就去做了下,然后发现并不会做,就搜了题解. 题解: 参考http://www.cnblogs.com/qscqesze/p/5868047.html…

C. Gerald's Hexagon Time Limit: 2 Sec Memory Limit: 256 MB 题目连接 http://codeforces.com/contest/559/problem/A Description Gerald got a very curious hexagon for his birthday. The boy found out that all the angles of the hexagon are equal to . Then he me…

题目链接 这个题取模的时候挺坑的!!! 题意:div(x , b) / mod(x , b) = k( 1 <= k <= a).求x的和 分析: 我们知道mod(x % b)的取值范围为 1  - (b-1).那么我们可以从这一点入口来进行解题.. mod (x, b) = 1 时, x  =  b + 1, 2b + 1, 3b + 1..... a * b + 1. mod (x , b) = 2 时, x =  2b + 2, 4b + 2, 6b + 2, ..... 2a * b…

A. Pasha and Stick 题目连接: http://www.codeforces.com/contest/610/problem/A Description Pasha has a wooden stick of some positive integer length n. He wants to perform exactly three cuts to get four parts of the stick. Each part must have some positive…