MaximumDepthOfBinaryTree.java

/*
Given the root of a binary tree, return its maximum depth.
A binary tree's maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node.

Example 1:
Input: root = [3,9,20,null,null,15,7]
Output: 3
 */

public class MaximumDepthOfBinaryTree {
    public static void main(String[] args) {
        TreeNode root=new TreeNode(3);
        root.left=new TreeNode(9);
        root.right=new TreeNode(20);
        root.left.left=null;
        root.left.right=null;
        root.right.left=new TreeNode(15);
        root.right.right=new TreeNode(7);
        int ans = maxDepth(root);
        System.out.println(ans);
    }
    public static int maxDepth(TreeNode root) {
        if (root==null){
            return 0;
        }
        return 1+Math.max(maxDepth(root.left),maxDepth(root.right));
    }
}
class TreeNode{
    int data;
    TreeNode left,right;
    public TreeNode(int key){
        key=data;
        left=right=null;
    }
}