Problem F: Alice and Bob
Description
Alice and Bob like playing games very much.Today, they introduce a new game.
There is a polynomial like this: (a0*x^(2^0)+1) * (a1 * x^(2^1)+1)*.......*(an-1 * x^(2^(n-1))+1). Then Alice ask Bob Q questions. In the expansion of the Polynomial, Given an integer P, please tell the coefficient of the x^P.
Can you help Bob answer these questions?
Input
The first line of the input is a number T, which means the number of the test cases.
For each case, the first line contains a number n, then n numbers a0, a1, .... an-1 followed in the next line. In the third line is a number Q, and then following Q numbers P.
1 <= T <= 20
1 <= n <= 50
0 <= ai <= 100
Q <= 1000
0 <= P <= 1234567898765432
Output
For each question of each test case, please output the answer module 2012.
Sample Input
1
2
2 1
2
3
4
Sample Output
2
0
HINT
The expansion of the (2*x^(2^0) + 1) * (1*x^(2^1) + 1) is 1 + 2*x^1 + 1*x^2 + 2*x^3
解题思路:完全靠位运算即可,可记住这个规律。
求多项式相乘展开式中x的某一指数的系数。
(a0*x^(2^0)+1) * (a1 * x^(2^1)+1)*.......*(an-1 * x^(2^(n-1))+1)给定这个式子,观察x的指数,2^0 2^1 2^2 。。很容易联想到二进制。
后来发现有规律,展开式中没有指数相同的两项,也就是说不能合并公因式。而某一x指数的系数化为二进制以后就可以找到规律了。
比如 求指数为13的系数,把13化为二进制 1 1 0 1 从右到左分别对应 a0 a1 a 2 a3 ,那么所求系数就是 a0 * a2 * a 3
再举例说明:
#include <iostream>
#include <stack>
#include <string.h>
using namespace std;
int a[];
int t,n,q;
long long p; int main()
{
cin>>t;while(t--)
{
cin>>n;
for(int i=;i<n;i++)
cin>>a[i];
cin>>q;
while(q--)
{
stack<int>s;
cin>>p;
int result=;
int cnt=-; //这里使用了-1,为了方便,因为a数组是从0开始的
int yu;
while(p) //把数化为二进制存到栈中
{
cnt++;
yu=p%;
s.push(yu);
p/=;
}
if(cnt>n-) //当数的二进制位数大于n时,不存在直接输出0
{
cout<<<<endl;
continue;
}
else
{
while(!s.empty())
{
if(s.top()==)
{
result*=a[cnt];//取数相乘
if(result>)
result%=;
}
s.pop();
cnt--;
}
}
cout<<result<<endl;
}
}
return ;
}