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#include <iostream>
int prod(int m, int n) {
if (m > n)
return -1;
int prod = m;
do {
m++;
prod *= m;
} while (m < n);
return prod;
}
int prod_r(int m, int n) {
if (m > n)
return -1;
if (m == n-1)
return m * n;
else
return m * prod_r(++m, n);
}
int fac(int n) {
int fac = n;
while (n > 1) {
n--;
fac *= n;
}
return fac;
}
int fac_r(int n) {
if (n == 0)
return 1;
return n * fac_r(--n);
}
int binom1(int m, int n) {
if (m < n)
return 0;
return fac(m) / (fac(n) * fac(m-n));
}
int binom2(int m, int n) {
return prod(n, m) * (m-n + 1) / fac(n);
}
int main() {
int x = 2, y = 4;
std::cout << "Product: " << prod(x,y) << std::endl;
std::cout << "Product: " << prod_r(x,y) << std::endl;
std::cout << "Faculty: " << fac(x) << std::endl;
std::cout << "Faculty: " << fac_r(x) << std::endl;
std::cout << "Binom 1: " << binom1(y,x) << std::endl;
std::cout << "Binom 2: " << binom2(y,x) << std::endl;
return 0;
}
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