display.cpp

#include<iostream>
#include<vector>
#include<stack>
using namespace std;

class Node{
public:
    int data;
    vector<Node*> children;

Node(int data){
    this-> data = data;
}

};

Node* input(){
    stack<Node*> *stk = new stack<Node*>; 
    int element, root_data, size;
    cin >> size >> root_data;
    Node *root = new Node(root_data);
    stk-> push(root);
    while(!stk-> empty()){
        cin >> element;
        if(element == -1){
            stk-> pop();
        }
        else{
            Node *new_node = new Node(element);
            stk->top()-> children.push_back(new_node);
            stk-> push(new_node);
        }
    }
    return root;
}

void display(Node *root){
    cout << root-> data << " ==> {";
    for(int i = 0 ;i < root-> children.size(); i++){
        cout << root-> children[i]->data << ',';
    }
    cout << ".}" << '\n';
    for(int i = 0; i < root-> children.size(); i++){
        display(root-> children[i]);
    } 
}

int main(){
    Node* root = input();
    display(root);
}