题目大意: 我们有一个集合 S,其中包含了 m 个不完全相同的区间[l1,r1],[l2,r2]…[lm,rm] (1≤li≤ri≤n,li,ri 都为整数). 定义 f(S)=k,表示集合 S 中能取出最多 k 个区间,使得这 k 个区间两两不相交. 问当 f(S)=k 时,符合条件的集合 S 有多少个. 思路: f[i][j]表示集合S中所有区间的端点均小于等于i且f(S)=j的集合S的个数. 显然i≥j,则f[i][j]由f[k][j-1](j-1≤k≤i)转移而来,新的与之前区间不相交的…
discription Sereja painted n points on the plane, point number i (1 ≤ i ≤ n) has coordinates (i, 0). Then Sereja marked each point with a small or large English letter. Sereja don't like letter "x", so he didn't use it to mark points. Sereja thi…
题目链接:http://codeforces.com/problemset/problem/627/A 题意: 告诉你s 和 x,a + b = s a xor b = x a, b > 0. 让你求符合条件的a b有多少对 思路: a + b = s , a ^ b = x ==> s - x = (a & b) * 2 #include <bits/stdc++.h> using namespace std; typedef long long LL;…
A. Anastasia and pebbles time limit per test:1 second memory limit per test:256 megabytes input:standard input output:standard output Anastasia loves going for a walk in Central Uzhlyandian Park. But she became uninterested in simple walking, so she…
Sereja has a sequence that consists of n positive integers, a1, a2, ..., an. First Sereja took a piece of squared paper and wrote all distinct non-empty non-decreasing subsequences of sequence a. Then for each sequence written on the squared paper, S…
Sereja and Cinema 首先我们可以发现除了第一个人, 其他人都会坐在已入坐人的旁边. 难点在于计算方案数.. 我们可以从外往里把确定的人用组合数算上去,然后缩小范围. #include<bits/stdc++.h> #define LL long long #define LD long double #define fi first #define se second #define mk make_pair #define PLL pair<LL, LL> #de…
There are n cities and n - 1 roads in the Seven Kingdoms, each road connects two cities and we can reach any city from any other by the roads. Theon and Yara Greyjoy are on a horse in the first city, they are starting traveling through the roads. But…
题目链接:http://codeforces.com/problemset/problem/215/B Description The World Programming Olympics Medal is a metal disk, consisting of two parts: the first part is a ring with outer radius of r1 cm, inner radius of r2 cm, (0 < r2 < r1) made of metal wi…
地址:http://codeforces.com/contest/660/problem/A 题目: A. Co-prime Array time limit per test 1 second memory limit per test 256 megabytes input standard input output standard output You are given an array of n elements, you must make it a co-prime array…
传送门: http://codeforces.com/problemset/problem/598/A A. Tricky Sum time limit per test 1 second memory limit per test 256 megabytes input standard input output standard output In this problem you are to calculate the sum of all integers from 1 to n, b…
