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| #include <cstdio>
#include <cmath>
#include <algorithm>
using namespace std;
const double PI = acos(-1);
const int N = 5e6 + 10;
struct Complex
{
double x, y;
Complex() {}
Complex(double _x, double _y)
{
x = _x;
y = _y;
}
Complex operator+(Complex k)
{
return Complex(x + k.x, y + k.y);
}
Complex operator-(Complex k)
{
return Complex(x - k.x, y - k.y);
}
Complex operator*(Complex k)
{
return Complex(x * k.x - y * k.y, x * k.y + y * k.x);
}
} A[N], B[N];
int n, m, bit, tot, rev[N], ans[N];
void fft(Complex *x, int op)
{
for (int i = 0; i < tot; i++)
if (rev[i] < i)
swap(x[rev[i]], x[i]);
for (int mid = 1; mid < tot; mid <<= 1)
{
Complex w1 = Complex(cos(PI / mid), sin(op * PI / mid));
for (int i = 0; i < tot; i += (mid << 1))
{
Complex cur = Complex(1, 0);
for (int j = 0; j < mid; j++, cur = cur * w1)
{
Complex p = x[i + j], q = cur * x[i + j + mid];
x[i + j] = p + q, x[i + j + mid] = p - q;
}
}
}
}
void read(int &len, Complex *x)
{
char c;
while (~scanf("%c", &c) && (c > '9' || c < '0'))
;
do
x[len++].x = c - '0';
while (~scanf("%c", &c) && (c <= '9' && c >= '0'));
for (int i = 0, j = len - 1; i < j; i++, j--)
swap(x[i], x[j]);
}
int main()
{
read(n, A);
read(m, B);
while ((1 << bit) < n + m + 1)
bit++;
tot = 1 << bit;
for (int i = 0; i < tot; i++)
rev[i] = (rev[i >> 1] >> 1) | ((i & 1) << bit - 1);
fft(A, 1);
fft(B, 1);
for (int i = 0; i < tot; i++)
A[i] = A[i] * B[i];
fft(A, -1);
for (int i = 0; i <= n + m; i++)
ans[i] = A[i].x / tot + 0.5;
for (int i = 0; i < n + m; i++)
{
ans[i + 1] += ans[i] / 10;
ans[i] %= 10;
}
bool flag = false;
for (int i = n + m - 1; i >= 0; i--)
{
flag |= ans[i];
if (flag)
printf("%d", ans[i]);
}
return 0;
}
|