Problem
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
Solution
class Solution {
public int countNodes(TreeNode root) {
if (root == null) return 0;
int height = 0;
TreeNode left = root.left, right = root.right;
while (left != null && right != null) {
height++;
left = left.left;
right = right.right;
}
if (left == null && right == null) return (1 << (height+1)) - 1;
else return 1 + countNodes(root.left) + countNodes(root.right);
}
}
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