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average-of-levels-in-binary-tree

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Average of Levels in Binary Tree – LeetCode 637

Problem

Description

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

Answer

Original

Code

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/**
 * 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> ans;
        queue<TreeNode*> q;
        q.push(root);
        unsigned S;
        double level;
        TreeNode *now;
        while(!q.empty()){
            S = q.size();
            level = 0.0;
            for(int i = 0; i != S; ++i){
                level += q.front()->val;
                if(q.front()->left) q.push(q.front()->left);
                if(q.front()->right) q.push(q.front()->right);
                q.pop();
            }
            ans.emplace_back(level / S);
        }
        return ans;
    }
};

思路

简单的BFS。时间复杂度$O(n)$，空间复杂度$O(m)$。
耗时$8$ ms，排名$0.70\%$