動機
複習bfs
Problem
Given the root
of a binary tree, return the average value of the nodes on each level in the form of an array. Answers within 10-5
of the actual answer will be accepted.
Example 1:
Input: root = [3,9,20,null,15,7]Output: [3.00000,14.50000,11.00000]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].
Example 2:
<img alt="" src=“https://assets.leetcode.com/uploads/2021/03/09/avg2-tree.jpg “style=“width: 292px; height: 302px;” />Input: root = [3,9,20,15,7]Output: [3.00000,14.50000,11.00000]
Constraints:
- The number of nodes in the tree is in the range
[1, 104]
. -231 <= Node.val <= 231 - 1
Sol
class Solution:
def averageOfLevels(self, root: TreeNode) -> List[float]:
q = deque([[root]])
ret = []
while q:
rs = q.popleft()
ret.append(sum([r.val for r in rs])/len(rs))
next_rs = sum([[r.left, r.right] for r in rs],[])
next_rs = [r for r in next_rs if r]
if next_rs:
q.append(next_rs)
return ret