222. Count Complete Tree Nodes

Difficulty: Medium

Frequency: N/A

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.


My solution:
Data structure:
Steps:
Complexity:
Runtime:
Space:
Test cases:
Corner cases:
Code:
/**
 * 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) {
        int cnt = 0, h = height(root);
        while (root) {
            if (height(root->right) == h - 1) {
                cnt += 1 << h;
                root = root->right;
            } else {
                cnt += 1 << h - 1;
                root = root->left;
            }
            h--;
        }
        return cnt;
    }
    int height(TreeNode* node) {
        return !node ? -1 : 1 + height(node->left);
    }
};

Another solution:
Data structure:
steps:
Complexity:
Runtime:
Space:
Code:

Things to learn:
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