LeetCode in Net
222. Count Complete Tree Nodes
Medium
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:
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
using LeetCodeNet.Com_github_leetcode;
/**
* Definition for a binary tree node.
* public class TreeNode {
* public int val;
* public TreeNode left;
* public TreeNode right;
* public TreeNode(int val=0, TreeNode left=null, TreeNode right=null) {
* this.val = val;
* this.left = left;
* this.right = right;
* }
* }
*/
public class Solution {
public int CountNodes(TreeNode root) {
if (root == null) {
return 0;
}
int leftHeight = LeftHeight(root);
int rightHeight = RightHeight(root);
if (leftHeight == rightHeight) {
return (1 << leftHeight) - 1;
} else {
return 1 + CountNodes(root.left) + CountNodes(root.right);
}
}
private int LeftHeight(TreeNode root) {
if (root == null) {
return 0;
}
return 1 + LeftHeight(root.left);
}
private int RightHeight(TreeNode root) {
if (root == null) {
return 0;
}
return 1 + RightHeight(root.right);
}
}