方法數 C(n, k)
位數: 首數+1
#include <iostream>
#include <cmath>
using namespace std;
int main()
{
double n, k;
double LOG;
int digit;
while(cin >> n >> k)
{
LOG = 0;
k = min(k, n-k);
for(int i = 1; i<=k; i++)
LOG += log10((n-i+1)/i);
digit = floor(LOG);
cout << digit+1 << endl;
}
}
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