Top_View_of_Binary_Tree.cpp

#include <bits/stdc++.h>
using namespace std;

unordered_map<int, int> um;

struct Node
{
    int info;
    struct Node *left, *right;
};

struct Node *create()
{
    int data;
    Node *tree;
    tree = new Node;
    cout << "\nEnter data to be inserted or type -1 : ";
    cin >> data;

    if (data == -1)
        return 0;

    tree->info = data;

    cout << "Enter left child of " << data;
    tree->left = create();

    cout << "Enter right child of " << data;
    tree->right = create();

    return tree;
};

void topView(Node *root, int level)
{
    if (root == NULL)
        return;

    int i = um.count(level);

    if (i == 0)
        um[level] = root->info;

    topView(root->left, level - 1);
    topView(root->right, level + 1);

    um[level] = root->info;

    return;
}

int main()
{
    Node *root = NULL;
    root = create();

    topView(root, 0);

    for (auto x : um)
        cout << x.first << " --> " << x.second << endl;

    return 0;
}