package STS4007;

import java.util.*;

class TreeNode {

int data;

TreeNode left, right;

TreeNode(int data) {

this.data = data;

left = null;

right = null;

}

}

public class LeftView {

// Method to get the left view of the binary tree

static void leftView(TreeNode root, List<Integer> list, int level) {

if (root == null) {

return;

}

// If this is the first node of its level

if (level == list.size()) {

list.add(root.data);

}

// Recur for left and right subtrees

leftView(root.left, list, level + 1);

leftView(root.right, list, level + 1);

}

// Method to insert nodes in the binary tree level by level

static TreeNode buildTreeFromInput(Scanner sc) {

//

System.out.println("Enter the root value: ");

int rootVal = sc.nextInt();

TreeNode root = new TreeNode(rootVal);

Queue<TreeNode> queue = new LinkedList<>();

queue.add(root);

while (!queue.isEmpty()) {

TreeNode current = queue.poll();

System.out.println("Enter left child of " + current.data + " (or -1 if no left child): ");

int leftVal = sc.nextInt();

if (leftVal != -1) {

current.left = new TreeNode(leftVal);

queue.add(current.left);

}

System.out.println("Enter right child of " + current.data + " (or -1 if no right child): ");

int rightVal = sc.nextInt();

if (rightVal != -1) {

current.right = new TreeNode(rightVal);

queue.add(current.right);

}

}

return root;

}

public static void main(String[] args) {

Scanner sc = new Scanner(System.in);

// Build the tree from user input

TreeNode root = buildTreeFromInput(sc);

// List to store the left view

List<Integer> list = new ArrayList<>();

// Calculate the left view

leftView(root, list, 0);

// Print the left view

System.out.println("The left view is:");

for (int nodeVal : list) {

System.out.print(nodeVal + " ");

}

System.out.println();

sc.close();

}

}