886. 求组合数 II（模板）

import java.util.Scanner;

public class Main{
        static final int N=100005;
        static final int mod=(int)1e9+7;
        static long fact[]=new long[N];
        static long infact[]=new long[N];
        static long quick_pow(long a,long b){
                long res=1;
                while(b>0){
                        if((b&1)==1) res=res*a%mod;
                        a=a*a%mod;
                        b>>=1;
                }
                return res%mod;
        }
        public static void main(String[] args) {
                Scanner scan=new Scanner(System.in);
                fact[0]=infact[0]=1;
                for(int i=1;i<N;i++){
                        fact[i]=fact[i-1]*i%mod;
                        infact[i]=infact[i-1]*quick_pow(i,mod-2)%mod;
                }
               int t=scan.nextInt();
               while(t-->0){
                           int a=scan.nextInt();
                           int b=scan.nextInt();
                           System.out.println(fact[a]*infact[a-b]%mod*infact[b]%mod);
               }
        }
}