Submission #2611599

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Source Code Expand

#include<bits/stdc++.h>
using namespace std;

#define MOD 998244353


long long n,a,b,k;

long long fakt[300005], inv[300005];

long long komb(int a,int b){
	long long ret;
	//if(b > a) return 0;
	ret = fakt[a];
	ret = (ret * inv[b]) % MOD;
	ret = (ret * inv[a - b]) % MOD;
	return ret; 
}

long long pang(long long a,int b){
	if(b == 0) return 1;
	long long now = pang(a, b / 2);
	now = (now * now) % MOD;
	if(b % 2 == 1) now = (now * a) % MOD;
	return now;
}

int main(){
	cin >> n >> a >> b >> k;

	fakt[0] = 1;
	inv[0] = 1;
	fakt[1] = 1;
	inv[1] = 1;
	for(int i = 2; i <= 300000; i++){
		fakt[i] = (fakt[i - 1] * i) % MOD;
		inv[i] = pang(fakt[i], MOD - 2);
	}

	long long jaw = 0;
	for(long long i = 0; i <= 300000; i++){
		if(i > n) break;
		long long sisa = k - a * i;
		if(sisa % b != 0 || sisa < 0) continue;
		long long pake = sisa / b;
		if(pake > n) continue;

		long long tamb = (komb(n, i) * komb(n, pake)) % MOD;
	//	cout << i << " " << tamb << " here\n";
		jaw = (jaw + tamb) % MOD;
	}
	cout << jaw << "\n";
}

Submission Info

Judge Result