费马小定理+逆元(模板)


A - A
Time Limit:2000MS     Memory Limit:32768KB     64bit IO Format:%lld & %llu
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Description

Given n different objects, you want to take k of them. How many ways to can do it?

For example, say there are 4 items; you want to take 2 of them. So, you can do it 6 ways.

Take 1, 2

Take 1, 3

Take 1, 4

Take 2, 3

Take 2, 4

Take 3, 4

Input

Input starts with an integer T (≤ 2000), denoting the number of test cases.

Each test case contains two integers n (1 ≤ n ≤ 106), k (0 ≤ k ≤ n).

Output

For each case, output the case number and the desired value. Since the result can be very large, you have to print the result modulo 1000003.

Sample Input

3

4 2

5 0

6 4

Sample Output

Case 1: 6

Case 2: 1

Case 3: 15


F。模板题
#include  
#include  
#include  
#include  
#include  
#include  
#include  
#include  
#include  
#include  
#include  
using namespace std;  
const int INF=0x3f3f3f3f;  
typedef long long LL;  
const int mod=1e6+3;  
const int maxn=1e6+100;  
LL fac[maxn],inv[maxn];  
LL Pow(LL a,LL b)  
{  
    LL ans=1;  
    while(b)  
    {  
        if(b&1)  
            ans=(ans*a)%mod;  
        a=(a*a)%mod;  
        b>>=1;  
    }  
    return ans;  
}  
int main()  
{  
    int cas=0;  
    int n,a,b;  
    fac[0]=inv[0]=1;  
    for(int i=1;i<=1000000;i++)  
    {  
        fac[i]=(fac[i-1]*i)%mod; //对阶乘打表 
        inv[i]=Pow(fac[i],mod-2);  
    }  
    scanf("%d",&n);  
    while(n--)  
    {  
        scanf("%d%d",&a,&b);  
        LL ans=fac[a]*inv[b]%mod*inv[a-b]%mod;  
        printf("Case %d: %lld\n",++cas,ans);  
    }  
    return 0;  
}  

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