一个数 $n$ 必有一个不超过 $\sqrt n$ 的质因子. 打表处理出 $1$ 到 $\sqrt n$ 的质因子后去筛掉属于 $L$ 到 $R$ 区间的素数即可. Code: #include<cstdio> #include<cstring> #include<algorithm> #include<iostream> using namespace std; const int Range=50000; const int N=1000000+233…

The branch of mathematics called number theory is about properties of numbers. One of the areas that has captured the interest of number theoreticians for thousands of years is the question of primality. A prime number is a number that is has no prop…

题意:给一个数 可以写出多少种  连续素数的合 思路:直接线性筛 筛素数 暴力找就行   (素数到n/2就可以停下了,优化一个常数) 其中:线性筛的证明参考:https://blog.csdn.net/nk_test/article/details/46242401 https://blog.csdn.net/qq_40873884/article/details/79124552 https://blog.csdn.net/baoli1008/article/details/50788512…

Prime Distance Time Limit: 1000MS   Memory Limit: 65536K Total Submissions: 13961   Accepted: 3725 Description The branch of mathematics called number theory is about properties of numbers. One of the areas that has captured the interest of number th…

Description The branch of mathematics called number theory is about properties of numbers. One of the areas that has captured the interest of number theoreticians for thousands of years is the question of primality. A prime number is a number that is…

Description The branch of mathematics called number theory is about properties of numbers. One of the areas that has captured the interest of number theoreticians for thousands of years is the question of primality. A prime number is a number that is…

题目链接:poj 2689 Prime Distance 题意: 给你一个很大的区间(区间差不超过100w),让你找出这个区间的相邻最大和最小的两对素数 题解: 正向去找这个区间的素数会超时,我们考虑逆向思维: 我们先用线性筛 筛出前50000的素数,在int范围内的区间的合数的因子都在我们之前筛出来了, 然后我们就把这个区间的合数标记出来,剩下的就是素数了. 标记合数也是用全部的素数去筛一下,这样就能快速的标记这个区间的合数,然后在暴力枚举一下这个区间,更新一下答案. #include<cst…

2689 -- Prime Distance 没怎么研究过数论,还是今天才知道有素数二次筛法这样的东西. 题意是,要求求出给定区间内相邻两个素数的最大和最小差. 二次筛法的意思其实就是先将1~sqrt(b)内的素数先筛出来,然后再对[a,b]区间用那些筛出来的素数再次线性筛. 代码如下: #include <cstdio> #include <cstring> #include <algorithm> #include <iostream> using na…

题目链接:http://poj.org/problem?id=3126 题意: 给定两个四位素数 $a,b$,要求把 $a$ 变换到 $b$.变换的过程每次只能改动一个数,要保证每次变换出来的数都是一个没有前导零的四位素数. 要求每步得到的素数都不能重复,求从 $a$ 到 $b$ 最少需要变换多少步:如果无法达到则输出Impossible. 题解: 在BFS之前先用线性筛筛出 $10000$ 以内的素数,方便后面判断是否为素数. 剩下的就是从 $a$ 为起点,入队并标记已经出现过.每次队列非空就…

Prime Distance Time Limit: 1000MS   Memory Limit: 65536K Total Submissions: 12512   Accepted: 3340 Description The branch of mathematics called number theory is about properties of numbers. One of the areas that has captured the interest of number th…