ll A(ll n, ll r)//排列数
{ ll sum = 1;
for (int i = 0; i < r; i++)
sum *= n-i;
return sum;
}
ll C(ll n, ll r)//组合数
{ ll sum = 1;
for (int i = 1; i <= r; i++)
sum = sum * (n+1-i)/i;
return sum;
}
【组合数模板】
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转载自blog.csdn.net/qq_41037114/article/details/82842179
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