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.

代码如下：

 /**
  * Definition for a binary tree node.
  * public class TreeNode {
  *     int val;
  *     TreeNode left;
  *     TreeNode right;
  *     TreeNode(int x) { val = x; }
  * }
  */
 public class Solution {
     public int maxDepth(TreeNode root) {
         Stack<Integer> stack=new<Integer>Stack();

         int depth=0;
         if(root==null)
         return 0;
         if(root.left==null&&root.right==null)
         return 1;

         if(root.left!=null)
         {
             depth=1+maxDepth(root.left);

             if(stack.empty()||stack.peek()<depth)
             stack.push(depth);
         }

         if(root.right!=null)
         {
             depth=1+maxDepth(root.right);
             if(stack.empty()||stack.peek()<depth)
             stack.push(depth);
         }

         return stack.peek();
     }
 }