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  • [LeetCode] Average of Levels in Binary Tree

    Given a non-empty binary tree, return the average value of the nodes on each level in the form of an array.

    Example 1:

    Input:
        3
       / 
      9  20
        /  
       15   7
    Output: [3, 14.5, 11]
    Explanation:
    The average value of nodes on level 0 is 3,  on level 1 is 14.5, and on level 2 is 11. Hence return [3, 14.5, 11].

    Note:

    1. The range of node's value is in the range of 32-bit signed integer.

    题目要求一个非空二叉树的每一层数字和的平均值,并返回一个数组。首先想到的是二叉树的层次遍历,将每一层放去queue的数取平均值即可,需要注意的是int -> double的转换。

    class Solution {
    public:
        vector<double> averageOfLevels(TreeNode* root) {
            vector<double> res;
            double avg = 0;
            queue<TreeNode*> q;
            q.push(root);
            while (!q.empty()) {
                int n = q.size();
                double sum = 0;
                for (int i = 0; i != n; i++) {
                    TreeNode* node = q.front();
                    q.pop();
                    sum += node->val;
                    if (node->left != nullptr)
                        q.push(node->left);
                    if (node->right != nullptr)
                        q.push(node->right);
                }
                avg = sum / n;
                res.push_back(avg);
            }
            return res;
        }
    };
    // 16 ms
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  • 原文地址:https://www.cnblogs.com/immjc/p/7144396.html
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