CF-1009-E. Empty Triangle · znzryb
## 思路讲解
呃，这题虽然套着一个几何的背景，但我认为考察重点并不在几何上。
正解竟然就是随机化做法？这题的意义是什么那？我也不是很理解。
## AC代码
[https://codeforces.com/contest/2074/submission/318930035](https://codeforces.com/contest/2074/submission/318930035)
::: 源代码
```cpp
// Problem: E. Empty Triangle
// Contest: Codeforces - Codeforces Round 1009 (Div. 3)
// URL: https://codeforces.com/contest/2074/problem/E
// Memory Limit: 512 MB
// Time Limit: 2000 ms
// by znzryb
//
// Powered by CP Editor (https://cpeditor.org)
#include <bits/stdc++.h>
#define all(vec) vec.begin(),vec.end()
#define CLR(i,a) memset(i,a,sizeof(i))
#define fi first
#define se second
#define pb push_back
#define SZ(a) ((int) a.size())
#define FOR(i, a, b) for (int i = (a); i <= (b); ++i)
#define ROF(i, a, b) for (int i = (a); i >= (b); --i)
#define getFro(vec) (vec.empty()?0:vec.front())
#define getBac(vec) (vec.empty()?0:vec.front())
#define debug(var) cerr << #var <<":"<<var<<"\n";
#define DEBUG(variable) \
do { \
std::cerr << #variable << ":"; \
for (const auto& elem : variable) { \
std::cerr << elem << " "; \
} \
std::cerr << "\n"; \
} while (0)
#define uniVec(var) \
do { \
sort(var.begin(),var.end());\
var.resize(unique(var.begin(),var.end())-var.begin());\
} while (0)
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef __int128 i128;
typedef pair<ll,ll> pll;
typedef array<ll,3> arr;
typedef double DB;
typedef pair<DB,DB> pdd;
typedef pair<ll,bool> plb;
constexpr ll MAXN=static_cast<ll>(1e6)+10,INF=static_cast<ll>(1e18)+3;
constexpr ll mod=static_cast<ll>(1e9)+7;
constexpr double eps=1e-8;
ll N,M,K,T,A[MAXN];
inline void solve(){
cin>>N;
if(N==3){
cout<<"! 1 2 3"<<endl;
return;
}
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
uniform_int_distribution<> distrib(1,N),dis3(0,2);
vector<ll> quer={distrib(rng),distrib(rng),distrib(rng)};
while(quer[0]==quer[1] || quer[1]==quer[2] || quer[0]==quer[2]){
quer={distrib(rng),distrib(rng),distrib(rng)};
}
ll idx=0;
while(true){
cout<<"? "<<quer[0]<<" "<<quer[1]<<" "<<quer[2]<<endl;
ll res;
cin>>res;
if(res==0){
cout<<"! "<<quer[0]<<" "<<quer[1]<<" "<<quer[2]<<endl;
break;
}else{
quer[dis3(rng)]=res;
++idx;
}
}
}
int main()
{
ios::sync_with_stdio(false);
cin.tie(0);cout.tie(0);
cin>>T;
while(T--){
solve();
}
// solve();
return 0;
}
/*
TLE https://codeforces.com/contest/2074/submission/318917809
AC https://codeforces.com/contest/2074/submission/318930035
*/
```
:::
## 心路历程（WA，TLE，MLE……）
TLE
[https://codeforces.com/contest/2074/submission/318918084](https://codeforces.com/contest/2074/submission/318918084)
::: 源代码
```cpp
// Problem: E. Empty Triangle
// Contest: Codeforces - Codeforces Round 1009 (Div. 3)
// URL: https://codeforces.com/contest/2074/problem/E
// Memory Limit: 512 MB
// Time Limit: 2000 ms
// by znzryb
//
// Powered by CP Editor (https://cpeditor.org)
#include <bits/stdc++.h>
#define all(vec) vec.begin(),vec.end()
#define CLR(i,a) memset(i,a,sizeof(i))
#define fi first
#define se second
#define pb push_back
#define SZ(a) ((int) a.size())
#define FOR(i, a, b) for (int i = (a); i <= (b); ++i)
#define ROF(i, a, b) for (int i = (a); i >= (b); --i)
#define getFro(vec) (vec.empty()?0:vec.front())
#define getBac(vec) (vec.empty()?0:vec.front())
#define debug(var) cerr << #var <<":"<<var<<"\n";
#define DEBUG(variable) \
do { \
std::cerr << #variable << ":"; \
for (const auto& elem : variable) { \
std::cerr << elem << " "; \
} \
std::cerr << "\n"; \
} while (0)
#define uniVec(var) \
do { \
sort(var.begin(),var.end());\
var.resize(unique(var.begin(),var.end())-var.begin());\
} while (0)
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef __int128 i128;
typedef pair<ll,ll> pll;
typedef array<ll,3> arr;
typedef double DB;
typedef pair<DB,DB> pdd;
typedef pair<ll,bool> plb;
constexpr ll MAXN=static_cast<ll>(1e6)+10,INF=static_cast<ll>(1e18)+3;
constexpr ll mod=static_cast<ll>(1e9)+7;
constexpr double eps=1e-8;
ll N,M,K,T,A[MAXN];
inline void solve(){
cin>>N;
if(N==3){
cout<<"! 1 2 3"<<endl;
return;
}
vector<ll> quer={1,2,3};
ll idx=0;
while(true){
cout<<"? "<<quer[0]<<" "<<quer[1]<<" "<<quer[2]<<endl;
ll res;
cin>>res;
if(res==0){
cout<<"! "<<quer[0]<<" "<<quer[1]<<" "<<quer[2]<<endl;
break;
}else{
quer[idx%3]=res;
++idx;
}
}
}
int main()
{
ios::sync_with_stdio(false);
cin.tie(0);cout.tie(0);
cin>>T;
while(T--){
solve();
}
// solve();
return 0;
}
/*
TLE https://codeforces.com/contest/2074/submission/318917809
*/
```
:::