金点石成金

题目分析：

  1. 会增加ai的财富，消耗bi的魔法
  2. 回复ci的魔法，但减少di的财富
  3. 从1到n进行深搜，枚举所有情况，然后到最后去最大值

代码如下:

#include<bits/stdc++.h>

using namespace std;

#define  mm(a,x) memset(a,x,sizeof a)
#define  mk make_pair
#define ll long long
#define pii pair<int,int>
#define inf 0x3f3f3f3f
#define lowbit(x) (x) & (-x)

const int N = 20;

int n;
struct Node{
    ll a,b,c,d;
}node[N];
ll ans;

void dfs(int u,ll money,ll magic){
    if(u == n + 1){
        ans = max(ans,money * magic);
        return ;
    }
    ll t = magic - node[u].b;
    if(t < 0) t = 0;
    dfs(u + 1,money + node[u].a,t);
    t = money - node[u].d;
    if(t < 0) t = 0;
    dfs(u + 1,t,magic + node[u].c);
}
int main() {
    cin >> n;
    for(int i = 1; i <= n; i ++ ){
        ll a,b,c,d; cin >> a >> b >> c >> d;
        node[i] = {a,b,c,d};
    }
    dfs(1,0,0);
    cout<<ans;    
    return 0;
}