谁能帮我看看玄学代码

#include<bits/stdc++.h>
#include <math.h>
#define pr(x) cerr<<#x<<"="<<(x)<<endl
#define pri(x,lo) {cerr<<#x<<"={";for (int ol=0;ol<=lo;ol++)cerr<<x[ol]<<",";cerr<<"}"<<endl;}
#define ll long long
using namespace std;
const int Inf=1e5+1;
ll a[Inf],f[Inf],V,n;
struct E{
	ll a,b,c;
}e[Inf];
bool cmp(E x,E y){
	return y.b*x.c>x.b*y.c;
}
int main(){
	scanf("%lld%lld",&V,&n);
	for(int i=1;i<=n;i++){
		scanf("%lld",&e[i].a);
	}
	for(int i=1;i<=n;i++){
		scanf("%lld",&e[i].b);
	}
	for(int i=1;i<=n;i++){
		scanf("%lld",&e[i].c);
	}
	sort(e+1,e+n+1,cmp);
	for(int i=1;i<=n;i++){
		for(ll j=V;j>=e[i].c;j--){
			f[j]=max(f[j],f[j-e[i].c]+e[i].a-(V-(j-e[i].c))*e[i].b);
		}
	}
	printf("%lld",f[V]);
	return 0;
}
/*
1:bycx
2:bxcy
*/