UVALIVE6886 Golf Bot (FFT)

题意:打高尔夫 给你n个距离表示你一次可以把球打远的距离

　　 然后对于m个询问 问能否在两杆内把球打进洞

题解:平方一下就好 注意一下x0的系数为1表示打一杆

　　 才发现数组应该开MAXN * 4 之前写的题数据有点不严谨了

#include <stdio.h>
#include <algorithm>
#include <iostream>
#include <math.h>
using namespace std;
const double PI = acos(-1.0);
const double eps = 1e-;

struct Complex
{
    double x, y;
    Complex(double _x = 0.0, double _y = 0.0)
    {
        x = _x;
        y = _y;
    }
    Complex operator + (const Complex &b) const
    {
        return Complex(x + b.x, y + b.y);
    }
    Complex operator - (const Complex &b) const
    {
        return Complex(x - b.x, y - b.y);
    }
    Complex operator * (const Complex &b) const
    {
        return Complex(x * b.x - y * b.y, x * b.y + y * b.x);
    }
};

void change(Complex y[], int len)
{
    int i, j, k;
    for(i = , j = len / ; i < len - ;i++)
    {
        if(i < j) swap(y[i], y[j]);
        k = len / ;
        while(j >= k)
        {
            j -= k;
            k /= ;
        }
        if(j < k) j += k;
    }
}

void fft(Complex y[], int len, int on)
{
    change(y, len);
    for(int h = ; h <= len; h <<= )
    {
        Complex wn(cos(-on *  * PI / h), sin(-on *  * PI / h));
        for(int j = ; j < len; j += h)
        {
            Complex w(, );
            for(int k = j; k < j + h / ; k++)
            {
                Complex u = y[k];
                Complex t = w * y[k + h / ];
                y[k] = u + t;
                y[k + h / ] = u - t;
                w = w * wn;
            }
        }
    }
    if(on == -)
        for(int i = ; i < len; i++)
            y[i].x /= len;
}

Complex x1[];

int main()
{
    int n, m;
    while(~scanf("%d", &n))
    {
        int zd = ;
        for(int i = ; i <= ; i++) x1[i] = Complex(, );
        for(int i = ; i <= n; i++)
        {
            int x; scanf("%d", &x);
            zd = max(zd, x);
            x1[x] = Complex(, );
        }
        x1[] = Complex(, );

        int len = ;
        while(len < zd + ) len <<= ;
        len <<= ;
        for(int i = zd + ; i < len; i++) x1[i] = Complex(, );

        fft(x1, len, );
        for(int i = ; i < len; i++) x1[i] = x1[i] * x1[i];
        fft(x1, len, -);

        scanf("%d", &m);
        int ans = ;
        for(int i = ; i <= m; i++)
        {
            int xx; scanf("%d", &xx);
            if(fabs(x1[xx].x) > eps) ans++;
        }
        printf("%d\n", ans);
    }
    return ;
}