Distance Code

#include <bits/stdc++.h>

using namespace std;

int n;

void encoder(){
  std::vector<int> ne (n, 0);
  std::vector<std::vector<pair<int, int> > > e (n);
  int a, b;
  for(int i=0; i<n-1; i++){
    cin >> a >> b;
    a--;
    b--;
    e[a].push_back({b, 1});
    e[b].push_back({a, 1});
    ne[a]++;
    ne[b]++;
  }
//  cout << "in"<<endl;
  int c=0;
  while (c<n) {
    for(int i=0; i<n; i++)
      if(ne[i]<=1){
        cout << i+1<< " ";
        c++;
        if(ne[i]==1){
          int j=-1;
          for(auto &x: e[i])
            if(x.second){
              j=x.first;
              x.second=0;
              break;
            }
          if(j==-1){
            cout << "j=-1"<<endl;
            return;
          }
          ne[j]--;
          for(auto &x: e[j])
            if(x.second && x.first==i){
              x.second=0;
              break;
            }
        }
        ne[i]=n;
      }
  }
  cout << endl;
}

int first=0, last=1;
std::vector<std::vector<int> > e;
std::vector<int> df;
std::vector<int> dl;

void connect(int i, int j){ //append j on i
  if(i==-1)
    return ;
  //cout << i << " c"<<j << endl;
  e[i].push_back(j);
  e[j].push_back(i);
  df[j]=df[i]+1;
  dl[j]=dl[i]+1;
  if(i==last){
    last=j;
    for(int &x: dl)
      x++;
    dl[j]=0;
  }
  if(i==first){
    first=j;
    for(int &x: df)
      x++;
    df[j]=0;
  }
}

int best(int i, int d){
  std::vector<pair<int, int>> st;
  std::vector<char> ma (n, 0);
  int p=-1, b=n;
  st.push_back({i, 0});
  while(!st.empty()){
    int a, dis;
    tie(a, dis)=st.back();
    st.pop_back();
  //  cout << a << "dfs "<<dis << endl;
    if(ma[a])
      continue;
    ma[a]=1;
    if(dis>=d)
      continue;
    if(dis==d-1){
      if(df[a]<b || dl[a]<b){
        p=a;
        b=df[a]<dl[a]?df[a]:dl[a];
      }
      if(p==first || p==last)
        return p;
    } else
      for(int &x: e[a])
        if(!ma[x])
          st.push_back({x, dis+1});
  }
//  cout << i << " best"<<d << " "<<p<<endl;
  if(p==-1)
    cout << "p=-1" << endl;
  return p;
}

void decoder(){
  e.resize(n);
  df.resize(n, 0);
  dl.resize(n, 0);
  std::vector<int> d(n-1, 0);
  //int a;
  for(int i=0; i<n-1; i++){
    cin >> d[i];
  }
  e[0].push_back(1);
  e[1].push_back(0);
  first=0;
  last=1;
  df[0]=dl[1]=0;
  dl[0]=df[1]=1;
  //cout << n << endl;
  for(int i=n-3; i>=0; i--){
//    cout << i << "for "<<d[i]<<endl;
    if(d[i]==1)
      connect(n-2-i, n-1-i);
    else
      connect(best(n-2-i, d[i]), n-1-i);
  }
  for(int i=0; i<n; i++)
    for(int &x: e[i])
      if(x>i)
        cout << i+1 <<" "<< x+1 <<endl;
}

int main(){
  ios_base::sync_with_stdio(false);
  int t;
  cin >> t >> n;
  if(t==1)
    encoder();
  else
    decoder();
}

Test 1

Group: 1, 2, 3

Verdict: ACCEPTED

Test 2

Group: 1, 2, 3

Verdict: ACCEPTED

Test 3

Group: 1, 2, 3

Verdict: ACCEPTED

Test 4

Group: 1, 2, 3

Verdict: ACCEPTED

Test 5

Group: 1, 2, 3

Verdict: ACCEPTED

Test 6

Group: 1, 2, 3

Verdict: ACCEPTED

Test 7

Group: 1, 2, 3

Verdict: ACCEPTED

Test 8

Group: 1, 2, 3

Verdict: ACCEPTED

Test 9

Group: 1, 2, 3

Verdict: ACCEPTED

Test 10

Group: 1, 2, 3

Verdict: ACCEPTED

Test 11

Group: 1, 2, 3

Verdict: ACCEPTED

Test 12

Group: 2, 3

Verdict: ACCEPTED

Test 13

Group: 2, 3

Verdict: ACCEPTED

Test 14

Group: 2, 3

Verdict: WRONG ANSWER

Test 15

Group: 2, 3

Verdict: WRONG ANSWER

Test 16

Group: 3

Verdict: TIME LIMIT EXCEEDED

Test 17

Group: 3

Verdict: TIME LIMIT EXCEEDED

Test 18

Group: 3

Verdict: WRONG ANSWER

Test 19

Group: 3

Verdict: WRONG ANSWER

Test 20

Group: 1, 2, 3

Verdict: ACCEPTED