DSA/src/com/dsa/trees/LevelOrderTraversal.java

package com.dsa.trees;

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import java.util.LinkedList;
import java.util.List;
import java.util.Queue;

public class LevelOrderTraversal {
    public static void main(String[] args) {
        try (BufferedReader reader = new BufferedReader(new FileReader("input.txt"))) {
            String[] elements = reader.readLine().trim().split(",");
            Queue<TreeNode> queue = new LinkedList<>();
            TreeNode root = new TreeNode(Integer.parseInt(elements[0]));
            queue.offer(root);
            int index = 1;
            while (!queue.isEmpty() && index < elements.length) {
                TreeNode node = queue.poll();
                if (!elements[index].equalsIgnoreCase("null")) {
                    node.left = new TreeNode(Integer.parseInt(elements[index]));
                    queue.offer(node.left);
                }
                index++;
                if (!elements[index].equalsIgnoreCase("null")) {
                    node.right = new TreeNode(Integer.parseInt(elements[index]));
                    queue.offer(node.right);
                }
                index++;
            }
            List<List<Integer>> list = levelOrderBottom(root);
            for (List<Integer> level : list) {
                System.out.println(level);
            }
            System.out.println("MinDepth: " + minDepth(root));
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }

    public static List<List<Integer>> levelOrder(TreeNode root) {
        List<List<Integer>> res = new LinkedList<>();
        if (root == null) return res;
        Queue<TreeNode> queue = new LinkedList<>();
        queue.offer(root);
        while (!queue.isEmpty()) {
            List<Integer> list = new LinkedList<>();
            int size = queue.size();
            for (int i = 0; i < size; i++) {
                TreeNode node = queue.poll();
                list.add(node.val);
                if (node.left != null) queue.offer(node.left);
                if (node.right != null) queue.offer(node.right);
            }
            res.add(list);
        }
        return res;
    }

    public static List<List<Integer>> levelOrderBottom(TreeNode root) {
        List<List<Integer>> res = new LinkedList<>();
        if (root == null) return res;
        Queue<TreeNode> queue = new LinkedList<>();
        queue.offer(root);
        while (!queue.isEmpty()) {
            List<Integer> list = new LinkedList<>();
            int size = queue.size();
            for (int i = 0; i < size; i++) {
                TreeNode node = queue.poll();
                list.add(node.val);
                if (node.left != null) queue.offer(node.left);
                if (node.right != null) queue.offer(node.right);
            }
            res.addFirst(list);
        }
        return res;
    }

    private static int diameter = 0;
    public static int diameterOfBinaryTree(TreeNode root) {
        diameter = 0;
        if (root == null) return 0;
        heightOfBT(root);
        return diameter - 1;
    }

    public static int heightOfBT(TreeNode root) {
        if (root == null) return 0;
        int leftHeight = heightOfBT(root.left);
        int rightHeight = heightOfBT(root.right);
        diameter = Math.max(leftHeight + rightHeight + 1, diameter);
        return Math.max(leftHeight, rightHeight) + 1;
    }

    public static int minDepth(TreeNode root) {
        if(root == null) return 0;
        int leftHeight = minDepth(root.left);
        int rightHeight = minDepth(root.right);
        if (leftHeight == 0) return rightHeight + 1;
        if (rightHeight == 0) return leftHeight + 1;
        return Math.min(leftHeight, rightHeight) + 1;
    }
}