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  1. #include<bits/stdc++.h>
  2. using namespace std;
  3. #define endl '\n'
  4. #define int long long
  5. const int MOD = pow(10,9)+7;
  6. const int MOD2 = 998244353;
  7. const int INF = LLONG_MAX/2;
  8.  
  9. int primes[1000000];
  10.  
  11. void seive(){
  12.     fill(primes, primes + 1000000, 1);
  13.     primes[0] = primes[1] = 0;
  14.     for(int i = 2 ; i*i < 1000000 ; i++){
  15.         if(primes[i]){
  16.             for(int j = i*i ; j < 1000000 ; j += i){
  17.                 primes[j] = 0;
  18.             }
  19.         }
  20.     }
  21.     for(int i = 1 ; i < 1000000 ; i++){
  22.         primes[i] += primes[i-1];
  23.     }
  24. }
  25. int factorial(int n){
  26.     if(n==0){
  27.         return 1;
  28.     }
  29.     return (n*(factorial(n-1)))%MOD;
  30. }
  31. bool isPrime(int n){
  32.     if(n <= 1) return false;
  33.     for(int i = 2 ; i*i <= n ; i++){
  34.         if(n % i == 0) return false;
  35.     }
  36.     return true;
  37. }
  38.  
  39. int power(int a, int b){
  40.     if(b == 0) return 1;
  41.     a %= MOD;
  42.     int value = power(a, b / 2);
  43.     if(b % 2 == 0){
  44.         return (value * value) % MOD;
  45.     } else {
  46.         return ((value * value) % MOD * (a % MOD)) % MOD;
  47.     }
  48. }
  49.  
  50. int gcd(int a, int b){
  51.     if(a == 0) return b;
  52.     return gcd(b % a, a);
  53. }
  54. void solve() {
  55.     int n1;
  56.     cin>>n1;
  57.     vector<int>A[n1+1];
  58.     for(int i = 0 ; i<n1-1 ; i++){
  59.         int a,b;
  60.         cin>>a>>b;
  61.         A[a].push_back(b);
  62.         A[b].push_back(a);
  63.     }
  64.     int d;
  65.     cin>>d;
  66.     queue<int>q;
  67.     int visited[n1+1] = {0};
  68.     int children[n1+1]={0};
  69.     visited[d] = 1;
  70.     q.push(d);
  71.     while(!q.empty()){
  72.         int node = q.front();
  73.         q.pop();
  74.         for(auto node1 : A[node]){
  75.             if(!visited[node1]){
  76.                 q.push(node1);
  77.                 visited[node1] = 1;
  78.                 children[node] = children[node]+1;
  79.             }
  80.             else{
  81.                 //parent
  82.             }
  83.         }
  84.     }
  85.     if(children[d]==3){
  86.     cout<<"The vertices that can be placed as root to make a valid binary tree is as follows: ";
  87.     for(int i = 1 ; i<=n1 ; i++){
  88.         if(children[i]==0){
  89.             cout<<i<<" ";
  90.         }
  91.     }
  92.     cout<<endl;
  93.     }
  94.     else{
  95.         cout<<"It is already a valid binary tree"<<endl;
  96.     }
  97. }
  98.  
  99. signed main(){
  100.     ios::sync_with_stdio(false); cin.tie(NULL);
  101.     //int t;
  102.     //cin >> t;
  103.     //while(t--){
  104.         solve();
  105.     //}
  106.     return 0;
  107. }
Success #stdin #stdout 0.01s 5320KB
comments (?)
stdin 
8
1 2
1 3
1 4
2 5
3 6
3 7 
4 8
1
stdout 
The vertices that can be placed as root to make a valid binary tree is as follows: 5 6 7 8
https://ideone.com/1GqNOh
language:
C++14 (gcc 8.3)
created:
15 hours ago
visibility:
public

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