104. Maximum Depth of Binary Tree

104. Maximum Depth of Binary Tree

Easy

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.

 对于给定的1个结点，如果不为空，那么depth就为1。

然后需要遍历左右子结点，分别得到depth，并且取其中较大的值。

只要左右子结点，有一个不为空，那就递归遍历。

public int MaxDepth(TreeNode root)
        {
            int depth;
            if (root == null)
            {
                depth = 0;
            }
            else
            {
                depth = 1;
                TreeNode left = root.left;
                TreeNode right = root.right;
                if (left != null || right != null)
                {
                    int leftDepth = MaxDepth(left);
                    int rightDepth = MaxDepth(right);
                    depth = depth + Math.Max(leftDepth, rightDepth);
                }
            }

            return depth;
        }