2022-11-15 Daily Challenge

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

November LeetCoding Challenge 15

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:

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

class Solution {
  int height(TreeNode *root) {
    if(!root) return -1;
    int h = 0;
    while(root) {
      h += 1;
      root = root->left;
    }
    return h-1;
  }
public:
    int countNodes(TreeNode* root) {
      if(!root) return 0;
      int h = height(root);
      return h < 0 ? 0 :
                     height(root->right) == h - 1 ? (1 << h) + countNodes(root->right) :
                                                    (1 << (h - 1)) + countNodes(root->left);
    }
};

// Accepted
// 18/18 cases passed (30 ms)
// Your runtime beats 97.25 % of cpp submissions
// Your memory usage beats 93.85 % of cpp submissions (30.7 MB)
Algorithm