222. Count Complete Tree Nodes

最新推荐文章于 2024-01-20 11:36:34 发布

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本文介绍了一种计算完全二叉树中节点数量的方法。通过递归算法结合数学公式，实现了高效计算。完全二叉树定义为除了最后一层外每层都填满节点，并且所有节点都在最左侧。

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.

class Solution {
public:
    int countNodes(TreeNode* root) {
        if(!root) return 0;
        int leftlevel = 0;
        int rightlevel = 0;
        TreeNode * Rootleft = root;
        TreeNode * Rootright = root;
        while(Rootleft)
        {
            leftlevel ++ ;
            Rootleft = Rootleft->left;
        }
        
        while(Rootright)
        {
            rightlevel ++;
            Rootright = Rootright->right;
        }
        
        if(leftlevel == rightlevel) return pow(2,leftlevel) - 1;
        return countNodes(root->left) + countNodes(root->right) + 1;
    }
};