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();
}
}