2025“钉耙编程”中国大学生算法设计暑期联赛（4）——回忆与展望 · znzryb

## 思路讲解

赛后自己想出来了

核心代码是

```cpp
    FOR(i,1,N){
        if(cnt[i]==0) continue;
        diff[cnt[i]+1]-=1;
        diff[1]+=1;
    }
    // 这个sum维护的就是出现次数
    // Sum[i] 表示出现次数大于等于i的数有Sum[i]个
    vll Sum(N+5);
    FOR(i,1,N){
        Sum[i]=Sum[i-1]+diff[i];
    }
    ll ans=jichu;ll lans=jichu;
    FOR(i,2,N){     // 枚举分为i条链的情况
        if(Sum[i]<=1) break;
        lans+=(Sum[i]-1)*X;
        lans-=Sum[i]*Y;
        lans+=Z;
        ans=max(lans,ans);
    }
```

## AC代码

[https://acm.hdu.edu.cn/contest/view-code?cid=1175&rid=12705](https://acm.hdu.edu.cn/contest/view-code?cid=1175&rid=12705)



::: 源代码

```cpp
// by Gospel_rock
#include <bits/stdc++.h>
#define all(vec) vec.begin(),vec.end()
#define pb push_back
#define EB emplace_back
#define EM emplace
#define FI first
#define SE second
#define SZ(a) ((int) a.size())
#define FOR(i, a, b) for (long long i = (a); i <= (b); ++i)
#define ROF(i, a, b) for (long long i = (a); i >= (b); --i)
#define debug(var) cerr << #var <<":"<<var<<"\n";
#define cend cerr<<"-----------\n"
#define lson(var) (var<<1)
#define rson(var) ((var<<1)+1)
#define fsp(x) fixed<<setprecision(x)

using namespace std;

using  ll = long long;using ull = unsigned long long;
using DB=double;using LD=long double;
// using i128 = __int128;
using pdd = pair<DB,DB>;using plb = pair<ll,bool>;
using pll = pair<ll,ll>;using vll=vector<ll>;using vb=vector<bool>;
using tll = tuple<ll,ll,ll>;
using vpll = vector<pll>;using vtll = vector<tll>;
using arr3 = array<ll,3> ;using arr2 = array<ll,2>;
constexpr ll MAXN=(ll)1e6+10,INF=(ll)1e17+9; // 1e18+9也是素数
constexpr ll mod=(ll)1e9+7; // 998244353;
constexpr double eps=1e-8;const double pi=acos(-1.0);
ll N,M,Q,X,K,T,lT,Y,Z;

inline void __();
signed main()
{
	ios::sync_with_stdio(false);
	cin.tie(0);cout.tie(0);
	
	cin>>lT;
	while(lT--)
		__();
	return 0;
}
/*

*/
inline void __(){
	cin>>N>>X>>Y>>Z;
	vll P(N),cnt(N+5);
    FOR(i,0,N-1){
        cin>>P[i];
        ++cnt[P[i]];
    }
    if(N==1){
        cout<<X<<"\n";
        return;
    }
    sort(all(P));
    vll diff(N+5);
    ll jichu=0;
    FOR(i,1,N-1){
        if(P[i]==P[i-1]){
            jichu+=Y;
        }else{
            jichu+=X;
        }
    }
    jichu+=X;
    FOR(i,1,N){
        if(cnt[i]==0) continue;
        diff[cnt[i]+1]-=1;
        diff[1]+=1;
    }
    // 这个sum维护的就是出现次数
    // Sum[i] 表示出现次数大于等于i的数有Sum[i]个
    vll Sum(N+5);
    FOR(i,1,N){
        Sum[i]=Sum[i-1]+diff[i];
    }
    ll ans=jichu;ll lans=jichu;
    FOR(i,2,N){     // 枚举分为i条链的情况
        if(Sum[i]<=1) break;
        lans+=(Sum[i]-1)*X;
        lans-=Sum[i]*Y;
        lans+=Z;
        ans=max(lans,ans);
    }
    cout<<ans<<"\n";
}
/*
AC
https://acm.hdu.edu.cn/contest/view-code?cid=1175&rid=12705

*/
```


:::


## 心路历程（WA，TLE，MLE……）