递归
二叉树的深度
http://www.nowcoder.com/questionTerminal/435fb86331474282a3499955f0a41e8b
public int TreeDepth(TreeNode root) {
if(root==null){
return 0;
}
int height=0;
height=Math.max(TreeDepth(root.left),TreeDepth(root.right))+1;
return height;
}
