Count Complete Tree Nodes
Description
Given the root
of a complete binary tree, return the number of the nodes in the tree.
According to Wikipedia, every level, except possibly the last, is completely filled in a complete binary tree, 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
.
Design an algorithm that runs in less than O(n)
time complexity.
Example 1:
![](https://assets.leetcode.com/uploads/2021/01/14/complete.jpg)
Input: root = [1,2,3,4,5,6] Output: 6
Example 2:
Input: root = [] Output: 0
Example 3:
Input: root = [1] Output: 1
Constraints:
- The number of nodes in the tree is in the range
[0, 5 * 104]
. 0 <= Node.val <= 5 * 104
- The tree is guaranteed to be complete.
Solution(javascript)
/**
* Definition for a binary tree node.
* function TreeNode(val, left, right) {
* this.val = (val===undefined ? 0 : val)
* this.left = (left===undefined ? null : left)
* this.right = (right===undefined ? null : right)
* }
*/
/**
* @param {TreeNode} root
* @return {number}
*/
var countNodes = function(root) {
return treeNodes(root);
function treeNodes(node){
if(!node){
return 0;
}else{
var leftDepth = 0;
var rightDepth = 0;
var leftChild = node.left;
while(leftChild){
leftDepth++;
leftChild = leftChild.left;
}
var rightChild = node.right;
while(rightChild){
rightDepth++;
rightChild = rightChild.right;
}
if(leftDepth === rightDepth){
return Math.pow(2, leftDepth + 1) - 1;
}else{
return treeNodes(node.left) + treeNodes(node.right) + 1;
}
}
}
};