Count Complete Tree Nodes
Count Complete Tree Nodes
题目
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.
思路
根据完全二叉树的性质，左子树和右子树必存在一个满树。如何判断满树，满树的结点如何计算。
解题
c++版1
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33/**
* Definition for a binary tree node.
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
int countNodes(TreeNode* root) {
if(!root)
return 0;
TreeNode *left=root->left;
TreeNode *right=root->right;
int ldepth=1;
int rdepth=1;
while(left){
ldepth++;
left=left->left;
}
while(right){
rdepth++;
right=right->right;
}
if(ldepth==rdepth)
return pow(2,ldepth)-1;
else
return countNodes(root->left)+countNodes(root->right)+1;
}
};
python版1
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27# Definition for a binary tree node.
# class TreeNode:
# def __init__(self, x):
# self.val = x
# self.left = None
# self.right = None
class Solution:
# @param {TreeNode} root
# @return {integer}
def countNodes(self, root):
if not root:
return 0
lt=root
rt=root
ldepth=0
rdepth=0
while lt:
ldepth+=1
lt=lt.left
while rt:
rdepth+=1
rt=rt.right
if ldepth==rdepth:
return 2**ldepth-1
else:
return self.countNodes(root.left)+self.countNodes(root.right)+1
