LeetCode637-二叉樹的層平均值

1.題目描述

給定一個非空二叉樹, 傳回一個由每層節點平均值組成的數組。

示例 1:

輸入:
    3
   / \
  9  20
    /  \
   15   7
輸出: [3, 14.5, 11]
解釋:第0層的平均值是 3,  第1層是 14.5, 第2層是 11. 是以傳回 [3, 14.5, 11].

注意：節點值的範圍在32位有符号整數範圍内。
           

2.代碼實作

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    vector<double> averageOfLevels(TreeNode* root) {
        vector<double> res;
        if(root == nullptr)
            return res;
        
        queue<TreeNode*> q;
        TreeNode *r = root;
        q.push(r);
        int cur_cnt = 1;
        int nextLevel_cnt = 0;
        int dequeue_cnt = 0;
        double sum = 0;
        while(!q.empty())
        {
            r = q.front();
            q.pop();
            dequeue_cnt++;
            if(r->left)
            {
                q.push(r->left);
                nextLevel_cnt++;
            }
            if(r->right)
            {
                q.push(r->right);
                nextLevel_cnt++;
            }
            
            if(cur_cnt == dequeue_cnt)
            {
                sum += r->val;
                res.push_back(sum/cur_cnt);
                cur_cnt = nextLevel_cnt;
                dequeue_cnt = 0;
                nextLevel_cnt = 0;
                sum = 0.0;
            }
            else
                sum += r->val;
        }
        return res;
    }
};