Language: C++

#include <bits/stdc++.h>
//#include <boost/multiprecision/cpp_int.hpp>
//#include <ext/pb_ds/assoc_container.hpp>
//#include <ext/pb_ds/tree_policy.hpp>
#pragma GCC optimize("O3")
#define REP(i,n) for(int i=0;i<n;i++)
#define REPP(i,n) for(int i=1;i<=n;i++)
#define ALL(obj) (obj).begin(), (obj).end()
#define EPS (1e-9)
#define INF (1e17)
#define PI (acos(-1))
//const double PI = acos(-1);
//const double EPS = 1e-15;
//long long INF=(long long)1E17;
#define i_7 (long long)(1e9+7)
//#define i_7 998'244'353
long mod(long a){
    long long c=a%i_7;
    if(c>=0)return c;
    return c+i_7;
}
long long po(long a, long b){
    if(b==0){
        return 1;
    }
    
    long long z = po(a,b/2);
    z = mod(z*z);
    if(b%2!=0){
        z = mod(a*z);
    }
    return z;
}

bool prime_(int n){
  if(n==1){
    return false;
  }else if(n==2){
    return true;
  }else{
    for(int i=2;i<=std::sqrt(n);i++){
      if(n%i==0){
        return false;
      }
    }
    return true;
  }
}

long long gcd_(long long a, long long b){
  if(a<b){
    std::swap(a,b);
  }
  if(a%b==0){
    return b;
  }else{
    return gcd_(b,a%b);
  }
}
 
long long lcm_(long long x, long long y){
  return (x/gcd_(x,y))*y;
}

//using namespace std;
//using namespace boost::multiprecision;
//using namespace __gnu_pbds;

vector<int> G[55];
typedef pair<int, int> P;
map<P, int> eid;
vector<int> eset;
bool dfs(int v, int tv, int p = -1){
  if(v == tv){
    return true;
  }
  for(int nv:G[v]){
    if(nv == p)continue;
    if(dfs(nv, tv, v)){
      eset.push_back(eid[P(v, tv)]);
      return true;
    }else{
      continue;
    }
  }
}
    
int main(){
  using namespace std;
  int n;
  cin>>n;
  int a[n-1], b[n-1];
  REP(i,n-1){
    cin>>a[i]>>b[i];
    a[i]--;b[i]--;
    G[a[i]].push_back(b[i]);
    G[b[i]].push_back(a[i]);
    eid[P(a[i], b[i])] = eid[P(b[i], a[i])] = i;
  }
  return 0;
}


Compiler output:
a.cc:69:1: error: 'vector' does not name a type
   69 | vector<int> G[55];
      | ^~~~~~
a.cc:70:9: error: 'pair' does not name a type
   70 | typedef pair<int, int> P;
      |         ^~~~
a.cc:71:1: error: 'map' does not name a type
   71 | map<P, int> eid;
      | ^~~
a.cc:72:1: error: 'vector' does not name a type
   72 | vector<int> eset;
      | ^~~~~~
a.cc: In function 'bool dfs(int, int, int)':
a.cc:77:14: error: 'G' was not declared in this scope
   77 |   for(int nv:G[v]){
      |              ^
a.cc:80:7: error: 'eset' was not declared in this scope
   80 |       eset.push_back(eid[P(v, tv)]);
      |       ^~~~
a.cc:80:22: error: 'eid' was not declared in this scope
   80 |       eset.push_back(eid[P(v, tv)]);
      |                      ^~~
a.cc:80:26: error: 'P' was not declared in this scope
   80 |       eset.push_back(eid[P(v, tv)]);
      |                          ^
a.cc: In function 'int main()':
a.cc:96:5: error: 'G' was not declared in this scope
   96 |     G[a[i]].push_back(b[i]);
      |     ^
a.cc:98:5: error: 'eid' was not declared in this scope
   98 |     eid[P(a[i], b[i])] = eid[P(b[i], a[i])] = i;
      |     ^~~
a.cc:98:9: error: 'P' was not declared in this scope
   98 |     eid[P(a[i], b[i])] = eid[P(b[i], a[i])] = i;
      |         ^
a.cc: In function 'bool dfs(int, int, int)':
a.cc:86:1: warning: control reaches end of non-void function [-Wreturn-type]
   86 | }
      | ^