2021-10-24 Daily-Challenge

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In: DailyChallenge

Today I have done leetcode's October LeetCoding Challenge with cpp.

October LeetCoding Challenge 24

Description

Count Complete Tree Nodes

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:

img

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 * 10^4].
  • 0 <= Node.val <= 5 * 10^4
  • The tree is guaranteed to be complete.

Solution

auto speedup = [](){
  cin.tie(nullptr);
  cout.tie(nullptr);
  ios::sync_with_stdio(false);
  return 0;
}();
class Solution {
public:
    int countNodes(TreeNode* root) {
      if(!root) return 0;
      TreeNode* left = root;
      TreeNode* right = root;
      int count = 0;
      while(left && right) {
        left = left->left;
        right = right->right;
        count += 1;
      }
      if(!left && !right) return (1 << count) - 1;
      return 1 + countNodes(root->left) + countNodes(root->right);
    }
};

// Accepted
// 18/18 cases passed (62 ms)
// Your runtime beats 13.83 % of cpp submissions
// Your memory usage beats 21.46 % of cpp submissions (30.9 MB)
Algorithm