HDU 4279 Number(数学题，找规律）

题目大意：

Here are two numbers A and B (0 < A <= B). If B cannot be divisible by A, and A and B are not co-prime numbers, we define A as a special number of B.

　　For each x, f(x) equals to the amount of x’s special numbers.

　　For example, f(6)=1, because 6 only have one special number which is 4. And f(12)=3, its special numbers are 8,9,10.

　　When f(x) is odd, we consider x as a real number.

　　Now given 2 integers x and y, your job is to calculate how many real numbers are between them.

解题思路：

所有的real number即是大于4的不是偶数平方的偶数或者奇数平方的奇数。

#include <iostream>
#include <cstring>
#include <cstdio>
#include <cmath>
#define LL long long
using namespace std;
LL solve(LL n)
{
	if(n <= 4) return 0;
	LL res = (n - 4) / 2;
	LL t = sqrt(n);
	if(t & 1) res ++;
	return res;
}
int main()
{
	LL l, r;
	int T;
	scanf("%d", &T);
	while(T--)
	{
		cin>>l>>r;
		cout<< solve(r) - solve(l-1)<<endl;
	}
	return 0;
}