poj1781找规律约瑟环

/*这题一开始用约瑟环的递推公式做，发现无限的超时，果断打表一看，前五十如下：
1 1
2 1
3 3
4 1
5 3
6 5
7 7
8 1
9 3
10 5
11 7
12 9
13 11
14 13
15 15
16 1
17 3
18 5
19 7
...
规律出来了，先用等比求和算出在第几个循环里面，再用等差数列递推式算出是该循环的第几个值*/
#include <iostream>
#include <cstdio>
#include <cstring>
#include <cmath>
using namespace std;
int x,z;
long long n;
long long optimized_pow_n(long long x, unsigned int n)
{
long long pw = 1;
while (n > 0) {
if (n & 1)        // n & 1 等价于 (n % 2) == 1
pw *= x;
x *= x;
n >>= 1;        // n >>= 1 等价于 n /= 2
}
return pw;
}
int main()
{
char str;
while(scanf("%d%c%d",&x,&str,&z))
{
if(x == 0 && z == 0)
break;
n = x * optimized_pow_n(10,z);
//printf("%lld**\n",n);
long long ansp;
for(int i = 0; i != -1; i++)
{
long long a;
a = optimized_pow_n(2,i-1) - 1;
if(n <= (a+1)*2 - 1)
{
n = n - a;
break;
}
}
printf("%lld\n",1 + 2 * (n - 1));
}
return 0;
}