求调悬关

#include<bits/stdc++.h>
#define int long long
#define IOS ios::sync_with_stdio(0);cin.tie(0);cout.tie(0);
using namespace std;
const int maxn=1e6+5,mod=1e9+7;
int t,n,m,fac[maxn],invf[maxn],s[maxn];
int qpow(int a,int b){
	int res=1;
	while(b){
		if(b&1)res=res*a%mod;
		a=a*a%mod;
		b>>=1;
	}
	return res;
}
signed main(){
	IOS
	fac[0]=1;
	for(int i=1;i<=maxn-5;i++)fac[i]=fac[i-1]*i%mod;
	invf[maxn-5]=qpow(fac[maxn-5],mod-2);
	for(int i=maxn-4;i>=0;i--)invf[i]=invf[i+1]*(i+1)%mod;
	s[0]=1;
	for(int i=1;i<=maxn-5;i++)s[i]=(s[i-1]+(i&1?-1:1)*invf[i]+mod)%mod;
	cin>>t;
	while(t--){
		cin>>n>>m;
		cout<<(fac[n]*invf[m]%mod*s[n-m]%mod)<<"\n";
	}
	return 0;
}