222 Count Complete Tree Nodes

1 题目

Given a complete binary tree, count the number of nodes.

Note:

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.

Example:

Input: 
    1
   / \
  2   3
 / \  /
4  5 6

Output: 6

2 尝试解

class Solution {
public:
    int countNodes(TreeNode* root) {
        if(root == NULL)return 0;
        int result = 0;
        queue<TreeNode*> saver;
        saver.push(root);
        while(!saver.empty()){
            queue<TreeNode*>temp;
            while(!saver.empty()){
                TreeNode* cur = saver.front();
                result += 1;
                saver.pop();
                if(cur->left != NULL) temp.push(cur->left);
                if(cur->right != NULL) temp.push(cur->right);
            }
            saver.swap(temp);
        }
        return result;
    }
};

3 标准解

class Solution {

public:

    int countNodes(TreeNode* root) {

        if(!root) return 0;

        int hl=0, hr=0;

        TreeNode *l=root, *r=root;

        while(l) {hl++;l=l->left;}

        while(r) {hr++;r=r->right;}

        if(hl==hr) return pow(2,hl)-1;

        return 1+countNodes(root->left)+countNodes(root->right);

    }

};