zoj 3629 Treasure Hunt IV 打表找规律

H - Treasure Hunt IV

Time Limit:2000MS     Memory Limit:65536KB     64bit IO Format:%lld & %llu

Description

　　Alice is exploring the wonderland, suddenly she fell into a hole, when she woke up, she found there are b - a + 1 treasures labled a from b in front of her.
　　Alice was very excited but unfortunately not all of the treasures are real, some are fake.
　　Now we know a treasure labled n is real if and only if [n/1] + [n/2] + ... + [n/k] + ... is even.
　　Now given 2 integers a and b, your job is to calculate how many real treasures are there.

Input

　　The input contains multiple cases, each case contains two integers a and b (0 <= a <= b <= 2⁶³-1) seperated by a single space. Proceed to the end of file.

Output

　　Output the total number of real treasure.

Sample Input

0 2
0 10

Sample Output

1
6

题意：给你一个Long long范围的区间，然后问里面有多少个数，满足n/1+n/2+n/k……加起来等于一个偶数
题解：首先打表，然后我们发现这种数是扎堆存在的，[0,1),[4,9),[16,25),……
然后我们就这样子找规律，然后一个等差数列求和就好啦！

LL solve(LL n)
{
    LL m = (LL)sqrt(n*1.0);
    LL sum=0;
    if(m%2==0) sum = n-m*m;
    if(m%2==1) m++;
    LL j=m/2;
    sum=sum-j+2*j*j;
   // sum=sum+2*j*j-j;
    return sum;
}
int main()
{
    LL n,m;
    while(scanf("%llu%llu",&n,&m)>0)
    {
        n++,m++;
        LL ans=solve(n-1);
        LL cur =solve(m);
        printf("%llu\n",cur-ans);
    }
    return 0;
}