链接:LeetCode636
给一个非空二叉树,返回每层的平均值组成的数组。
相关标签:树
解法:BFS迭代,层序遍历,计算每层的平均值记录到res数组,最后返回res数组。神奇的地方在于不能在累加的时候先除以count,而是先累加到一起再除,不然通不过case。
python:
# Definition for a binary tree node.
# class TreeNode:
# def __init__(self, x):
# self.val = x
# self.left = None
# self.right = None
import collections
class Solution:
def averageOfLevels(self, root: TreeNode) -> List[float]:
res = []
if not root:
return res
queue = collections.deque()
queue.append(root)
while queue:
result = 0
n = len(queue)
for _ in range(len(queue)):
p = queue.popleft()
result += p.val
if p.left:
queue.append(p.left)
if p.right:
queue.append(p.right)
res.append(result/n)
return res
C++:
/**
* 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) {
if (!root){
return {};
}
vector<double> res;
queue<TreeNode*> q{{root}};
while(!q.empty()){
double total = 0;
int count = q.size();
for (int i=0;i<count;i++){
TreeNode *p = q.front();
q.pop();
total += p->val;
if (p->left){
q.push(p->left);
}
if (p->right){
q.push(p->right);
}
}
res.push_back(total/count);
}
return res;
}
};
参考:
[LeetCode] 637. Average of Levels in Binary Tree 二叉树的层平均值