Question

能不能帮我写个 程序找出n个自然数（互不相等）中r个数的组合有多少种

Answer 1

#include

int g(int a, int b) {

int c;

while (b) {

c = a % b;

a = b;

b = c;

}

return a;

}

int C(int n, int r) {

int ans = 1;

int i, gc;

if (r > n || r < 0) return 0;

if (n - r < r) r = n - r;

for (i = 1; i <= r; i++) {

gc = g(n - i + 1, i);

ans /= i / gc;

ans *= (n - i + 1) / gc;

}

return ans;

}

int main() {

int n, r;

while (scanf("%d%d", n, r) == 2) {

printf("%dn", C(n, r));

}

}