leetcode 222. Count Complete Tree Nodes 统计节点个数---------- java

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.

 

统计完全二叉树的节点个数

 

 

递归实现。

/**
 * 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) {
        
        if (root == null){
            return 0;
        }
        int deep = 0;
        TreeNode node = root;
        while (node != null){
            node = node.left;
            deep++;
        }
        node = root;
        int height = 0;
        while (node != null){
            node = node.right;
            height++;
        }
        if (deep == height){
            return (1 << height) - 1;
        } else {
            return countNodes(root.left) + countNodes(root.right) + 1; 
        }
        
    }
    
    
    
}