C1000 有趣的小球题解

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

const int modd=1e9+7;

int n,p,q,k,cnt;
int a[100];

void dfs(int x,int sum){
	if (x==n+1){
		if (sum>=k)	cnt++,cnt%=modd;
		return ;
	}
	if (a[x]==0)	dfs(x+1,sum+p);
	else	dfs(x+1,sum+q);
	dfs(x+1,sum);
}

int main(){
	cin>>n>>p>>q>>k;
	for (int i=1;i<=n;i++)	cin>>a[i];
	dfs(1,0);
	cout<<cnt;
}