Given a complete binary tree, count the number of nodes.
Definition of a complete binary tree from Wikipedia:
In a complete binary tree every level, except possibly the last, is completely filled, and all nodes in the last level are as far left as possible. It can have between 1 and 2h nodes inclusive at the last level h.
代码如下：（超时）
/**
* 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 countNodes(TreeNode root) {
List<TreeNode> list=PreOrder(root);
return list.size(); }
public List<TreeNode> PreOrder(TreeNode root){
List<TreeNode> list=new ArrayList<>();
if(root==null)
return list; list.add(root);
if(root.left!=null)
list.addAll(PreOrder(root.left));
if(root.right!=null)
list.addAll(PreOrder(root.right));
return list;
}
}