#include<bits/stdc++.h>
using namespace std;
class Node {
public:
    int data;
    Node* left;
    Node* right;

    Node(int value) {
        data = value;
        left = nullptr;
        right = nullptr;
    }
};

Node* constructBinaryTree(vector<pair<int, int>>& edges) {
    unordered_map<int, Node*> nodeMap;
    Node* root = nullptr;

    // Create all the nodes and store them in the node map
    for (const auto& edge : edges) {
        int parentValue = edge.first;
        int childValue = edge.second;

        if (nodeMap.find(parentValue) == nodeMap.end()) {
            Node* parent = new Node(parentValue);
            nodeMap[parentValue] = parent;

            if (root == nullptr) {
                root = parent;
            }
        }

        Node* child = new Node(childValue);
        nodeMap[childValue] = child;
    }

    // Connect the nodes based on the edges
    for (const auto& edge : edges) {
        int parentValue = edge.first;
        int childValue = edge.second;

        Node* parent = nodeMap[parentValue];
        Node* child = nodeMap[childValue];

        if (parent->left == nullptr) {
            parent->left = child;
        } else {
            parent->right = child;
        }
    }

    return root;
}

// Helper function to print the binary tree in preorder traversal
void preorderTraversal(Node* root) {
    if (root != nullptr) {
        cout << root->data << " ";
        preorderTraversal(root->left);
        preorderTraversal(root->right);
    }
}

int main() {
    // Example usage
    vector<pair<int, int>> edges = {{1, 2}, {1, 3}, {2, 4}, {2, 5}, {3, 6}, {3, 7}};
    Node* root = constructBinaryTree(edges);

    cout << "Preorder traversal of the constructed binary tree: ";
    preorderTraversal(root);
    cout << endl;

    return 0;
}
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Read inputs from stdin

OneCompiler's C++ online compiler supports stdin and users can give inputs to programs using the STDIN textbox under the I/O tab. Following is a sample program which takes name as input and print your name with hello.

#include <iostream>
#include <string>
using namespace std;

int main() 
{
    string name;
    cout << "Enter name:";
    getline (cin, name);
    cout << "Hello " << name;
    return 0;
}

About C++

C++ is a widely used middle-level programming language.

  • Supports different platforms like Windows, various Linux flavours, MacOS etc
  • C++ supports OOPS concepts like Inheritance, Polymorphism, Encapsulation and Abstraction.
  • Case-sensitive
  • C++ is a compiler based language
  • C++ supports structured programming language
  • C++ provides alot of inbuilt functions and also supports dynamic memory allocation.
  • Like C, C++ also allows you to play with memory using Pointers.

Syntax help

Loops

1. If-Else:

When ever you want to perform a set of operations based on a condition If-Else is used.

if(conditional-expression) {
   //code
}
else {
   //code
}

You can also use if-else for nested Ifs and If-Else-If ladder when multiple conditions are to be performed on a single variable.

2. Switch:

Switch is an alternative to If-Else-If ladder.

switch(conditional-expression){    
case value1:    
 // code    
 break;  // optional  
case value2:    
 // code    
 break;  // optional  
......    
    
default:     
 code to be executed when all the above cases are not matched;    
}

3. For:

For loop is used to iterate a set of statements based on a condition.

for(Initialization; Condition; Increment/decrement){  
  //code  
}

4. While:

While is also used to iterate a set of statements based on a condition. Usually while is preferred when number of iterations are not known in advance.

while (condition) {  
// code 
}

5. Do-While:

Do-while is also used to iterate a set of statements based on a condition. It is mostly used when you need to execute the statements atleast once.

do {  
 // code 
} while (condition);

Functions

Function is a sub-routine which contains set of statements. Usually functions are written when multiple calls are required to same set of statements which increases re-usuability and modularity. Function gets run only when it is called.

How to declare a Function:

return_type function_name(parameters);

How to call a Function:

function_name (parameters)

How to define a Function:

return_type function_name(parameters) {  
 // code
}