MaximumDepthOfBinaryTree.java

package com.examplehub.leetcode.easy;

import com.examplehub.leetcode.TreeNode;
import java.util.LinkedList;
import java.util.Queue;

public class MaximumDepthOfBinaryTree {
  public static int solution1(TreeNode root) {
    if (root == null) {
      return 0;
    }
    int leftHeight = solution1(root.left);
    int rightHeight = solution1(root.right);
    return Math.max(leftHeight, rightHeight) + 1;
  }

  public static int solution2(TreeNode root) {
    if (root == null) {
      return 0;
    }
    Queue<TreeNode> queue = new LinkedList<>();
    queue.offer(root);
    int answer = 0;
    while (!queue.isEmpty()) {
      int size = queue.size();
      while (size > 0) {
        TreeNode node = queue.poll();
        assert node != null;
        if (node.left != null) {
          queue.offer(node.left);
        }
        if (node.right != null) {
          queue.offer(node.right);
        }
        size--;
      }
      answer++;
    }
    return answer;
  }
}