距离的总和 - y119777 - 博客园



距离的总和 - y119777 - 博客园

2017 搜狗校园招聘 距离的总和

题目描述:

时间限制:c/c++ 2000MS

定义两个大于2的偶数之间的距离,为这两个数之间质数的个数。从小到大输入n个大于2的偶数,输出所有数两两之间距离的总和(应该有n*(n-1)/2个距离,输出总和就好)。
输入
第一行是输入偶数的个数,最小为2,最大可能到几万。之后每行为一个偶数,最小是4,最大可能是几百万,不重复的升序排列。
输出
输入数据两两间距离的总和,这应该是一个不小于0的整数。

样例输入
3
4
6
12
样例输出
6
 
看到题目我的想法是预处理算出一个数前面有多少个质数,然后利用区间减法的性质,可以得到任意区间的质数的个数。然后就是数每一个小区出现的次数,不难得到,这个次数为(n - i)*i,然后从左到右扫描累加和即可。当时我没有做出来。内存超限。

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