104. Maximum Depth of Binary Tree

Given a binary tree, find its maximum depth.

The maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node.

Note: A leaf is a node with no children.

Example:

Given binary tree [3,9,20,null,null,15,7],

    3
   / \
  9  20
    /  \
   15   7

return its depth = 3.

终极无敌之递归

class Solution {
    public int maxDepth(TreeNode root) {
    if(root == null) return 0;
        return Math.max(maxDepth(root.left), maxDepth(root.right)) + 1;
        
    }
}

 或者联动Mindepth的方法，检查左右子节点是否为空，一一判断

class Solution {
    public int maxDepth(TreeNode root) {
    if(root == null)
        return 0;
       if(root.left == null) return 1+maxDepth(root.right);
         if(root.right == null) return 1+maxDepth(root.left);
        return 1+Math.max(maxDepth(root.right),maxDepth(root.left));
    }
}