[leetCode/JS] 222. Count Complete Tree Nodes

문제 설명

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.

 

입출력 예

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.

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내 솔루션

• 어제 DFS, BFS 같은 알고리즘 공부를 해두어서 쉬운 문제였다.

var countNodes = function(root) {
  let count = 0;
  const search = (root) => {
    if(!root) return
    count++;
    search(root.left)
    search(root.right)
  }

  search(root)
  return count
};

감상평

• 복잡하게 count 값을 리턴하는 형태로 할 수 있지만 그럼 귀찮기 때문에 전역으로 처리..