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.
Solution:
/**
* 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 ans = 0;
while(root!=null){
int leftHeight = height(root.left);
int rightHeight = height(root.right);
if(leftHeight==rightHeight){
root = root.right;
ans += 1<<leftHeight;
} else {
root = root.left;
ans += 1<<rightHeight;
}
}
return ans;
}
public int height(TreeNode root){
int height = 0;
while(root!=null){
height++;
root = root.left;
}
return height;
}
}