June Leetcoding Challenge(6.23)

LeetCode六月挑战（6.23 ）Count Complete Tree Nodes LeetCode 222 解题方案Given a complete binary tree, count the number of nodes.

Note:

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.

Example:

Input: 
    1
   / \
  2   3
 / \  /
4  5 6

Output: 6

思路

代码

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    public int countNodes(TreeNode root) {
        int left = leftNode(root);
        int right = rightNode(root);
        return left == right ? (1<<left) -1 : 1 + countNodes(root.left)+countNodes(root.right);
        
    }
    
    public int leftNode(TreeNode root){
        return root == null? 0:1+leftNode(root.left);
    }
    
    public int rightNode(TreeNode root){
        return root == null? 0:1+rightNode(root.right);
    }
}