Submission #21,750

2026-01-13 19:04:26

cpp17

Accepted 50/50

59ms

3564 KiB

// UUID: 5fa63421-7c13-46cb-a9ca-19c300545877
#include <bits/stdc++.h>
using namespace std;
#define ll long long
const ll M=1e9+7;

ll binpow(ll a, ll b) {
    if (b==0)return 1LL;
    ll c=binpow(a, b/2);
    if (b%2==1)return (((c*c)%M)*a)%M;
    else return (c*c)%M;
}

int main() {
	ll b, c;cin>>b>>c;
    vector<ll>fact(2*c+2,1),inv(2*c+2,1);
    for(int i=1;i<=2*c+1;i++){
        fact[i]=fact[i-1]*i;fact[i]%=M;
        inv[i]=binpow(fact[i],M-2);
    }
    cout<<((((fact[2*c-b-1]*inv[c-1])%M)*inv[c-b])%M-(((fact[2*c-b-1]*inv[c])%M)*inv[c-b-1])%M+M)%M;
}

	Sum	Test	Verdict		Time	Memory
base	50/50
		1	Accepted	0/0	1ms	316 KiB
		2	Accepted	0/0	2ms	316 KiB
		3	Accepted	2/2	1ms	316 KiB
		4	Accepted	3/3	1ms	316 KiB
		5	Accepted	3/3	1ms	316 KiB
		6	Accepted	3/3	1ms	316 KiB
		7	Accepted	3/3	2ms	316 KiB
		8	Accepted	3/3	2ms	508 KiB
		9	Accepted	3/3	2ms	316 KiB
		10	Accepted	3/3	2ms	316 KiB
		11	Accepted	3/3	4ms	564 KiB
		12	Accepted	3/3	8ms	804 KiB
		13	Accepted	3/3	13ms	820 KiB
		14	Accepted	3/3	54ms	3144 KiB
		15	Accepted	3/3	27ms	1744 KiB
		16	Accepted	3/3	59ms	3432 KiB
		17	Accepted	3/3	39ms	2100 KiB
		18	Accepted	3/3	57ms	3328 KiB
		19	Accepted	3/3	54ms	3564 KiB