Codeforces Round #257 (Div. 1) C Codeforces Round #257 (Div. 1) E CF450E C. Jzzhu and Apples time limit per test 1 second memory limit per test 256 megabytes input standard input output standard output Jzzhu has picked n apples from his big apple tre…

https://vjudge.net/problem/CodeForces-449C 题目大意:1-n编号的苹果两两一对,他们的最大公约数不为1,求这些对的最大匹配. ———————————————————————————————— 我们显然先把素数筛出来. 然后我们从后往前循环素数p,然后p,2p,3p(取过的自动不要)……这些数两两都可以成一对. 但是如果是奇数个,我们就抛掉2p,因为2p一定可以与其他2的倍数一对. 不知道怎么证明…… #include<cstdio> #include&…

嘟嘟嘟 这道题正解是怎么对的其实我也不清楚,总之靠感性理解吧. 首先当然要把1到n / 2的素数都筛出来,因为两两能配对的数一定都是这些素数的倍数.这也就说明对于(n / 2, n]的素数,他们一定不能配对,所以就不用筛他们了. 筛完后我们考虑怎么配对,对于一个素数的所有倍数xi,他们任意两个都可以配对,但是可能配对完后得到的总配对数会减少.因此我们从最大的素数开始两两配对,感性理解就是越大的素数的倍数就越少,因此先尽量满足配对方案少的素数,然后再处理配对方案多的素数. 还有一点,就是当xi的倍…

Jzzhu and Apples 从大的质因子开始贪心, 如果有偶数个则直接组合, 如果是奇数个留下那个质数的两倍, 其余两两组合. #include<bits/stdc++.h> #define LL long long #define fi first #define se second #define mk make_pair #define PLL pair<LL, LL> #define PLI pair<LL, int> #define PII pair&l…

/* http://codeforces.com/problemset/problem/449/C cf 449 C. Jzzhu and Apples 数论+素数+贪心 */ #include <cstdio> #include <algorithm> using namespace std; ; int is_prime[Nmax]; int book[Nmax]; int cnt[Nmax]; int n,ans; void get__prime() { ;i<=n;i…

E. Jzzhu and Apples time limit per test 1 second memory limit per test 256 megabytes input standard input output standard output Jzzhu has picked n apples from his big apple tree. All the apples are numbered from 1 to n. Now he wants to sell them to…

C. Jzzhu and Apples time limit per test 1 second memory limit per test 256 megabytes input standard input output standard output Jzzhu has picked n apples from his big apple tree. All the apples are numbered from 1 to n. Now he wants to sell them to…

E. Jzzhu and Apples time limit per test 1 second memory limit per test 256 megabytes input standard input output standard output Jzzhu has picked n apples from his big apple tree. All the apples are numbered from 1 to n. Now he wants to sell them to…

E. Jzzhu and Apples time limit per test: 1 seconds memory limit per test: 256 megabytes input: standard input output: standard output Jzzhu has picked \(n\) apples from his big apple tree. All the apples are numbered from \(1\) to \(n\). Now he wants…

题意简述 给出正整数n,你要把1-n之间的正整数分成尽可能多组,使得每一组两个数的最大公约数大于1;输出能分成最多组的个数,并按任意顺序输出每组的两个数. 很妙的一道题. 首先我们考虑去处理每个质数的倍数,那么这个质数一定是小于等于 n/2 的,不然它在 n 的范围内是不会有倍数的. 那么我们先把 $1~n/2$ 范围内的所有质数筛出来. 枚举质数 然后我们要怎么用质数去处理答案呢? 首先我们从大到小枚举这些质数,然后去枚举它的倍数. 然鹅这样复杂度不会炸么?不会. $O(\sigma_{i=2…