leetcode637 二叉树的层平均值

class Solution {
public:
    vector<double> averageOfLevels(TreeNode* root) {
        vector<double> res;
        queue<TreeNode*> q;
        if(root == nullptr) return res;
        q.push(root);
        while(!q.empty()){
            int size = q.size();
            double sum = 0;
            for(int i = 0; i < size; i++){
                TreeNode* cur = q.front();
                q.pop();
                sum += cur->val;
                if(cur->left) q.push(cur->left);
                if(cur->right) q.push(cur->right);
            }
            res.push_back(sum/size);
        }
        return res;
    }
};

递归：

class Solution {
private:
    void recursion(TreeNode* cur, int level, vector<double>& sums, vector<int>& counts){
        if(cur == nullptr) return;
        if(level >= sums.size()){
            sums.push_back(0);
            counts.push_back(0);
        }
        sums[level] += cur->val;
        counts[level]++;
        if(cur->left) recursion(cur->left, level+1, sums, counts);
        if(cur->right) recursion(cur->right, level+1, sums, counts);
    }
public:
    vector<double> averageOfLevels(TreeNode* root) {
        vector<double> sums;
        vector<int> counts;
        recursion(root, 0, sums, counts);
        vector<double> res;
        for (int i = 0; i < sums.size(); i++) {
            res.push_back(sums[i] / counts[i]); // 计算每层平均值
        }
        return res;
    }
};