一点简单数学知识
1.组合数
$C_a^b=\frac{a!}{b!(a-b)!}$
$C_a^b=C_{a-1}^b+C_{a-1}^{b-1}$
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| #include<bits/stdc++.h>
using namespace std;
const int N = 2010, mod = 1e9 + 7;
int c[N][N];
void init()
{
for(int i = 0; i < N; i ++)
for(int j = 0;j <= i;j ++)
if(!j) c[i][j] = 1;
else c[i][j] = (c[i - 1][j] + c[i - 1][j - 1]) % mod;
}
int main()
{
inti();
int n;
cin >> n;
while(n --)
{
int a, b;
cin >> a >> b;
cout << c[a][b] << endl;
}
return 0;
}
|
2.快速幂
