java 代码

import java.util.*;
import java.io.*;

class Main{
    static int N = 100010, n = 0, MOD = 1000000007;
    static int[] fact = new int[N], infact = new int[N];
    static int qmi(int a, int k, int p){
        int res = 1;
        while(k != 0){
            if((k & 1) != 0)res = (int)((long)res * a % p);
            a = (int)((long)a * a % MOD);
            k >>= 1;
        }
        return res;
    }
    public static void main(String[] args)throws Exception{
        BufferedReader buf = new BufferedReader(new InputStreamReader(System.in));
        n = Integer.valueOf(buf.readLine());
        fact[0] = infact[0] = 1;
        for(int i = 1; i < N; ++i){
            fact[i] = (int)((long)fact[i - 1] * i % MOD);
            infact[i] = (int)((long)infact[i - 1] * qmi(i, MOD - 2, MOD) % MOD);
        }
        while(n -- != 0){
            String[] info = buf.readLine().split(" ");
            int a = Integer.valueOf(info[0]);
            int b = Integer.valueOf(info[1]);
            System.out.println((int)((long)((long)fact[a] * infact[a - b] % MOD) * infact[b] % MOD));
        }
    }
}