102. Binary Tree Level Order Traversal
Given a binary tree, return the level order traversal of its nodes' values. (ie, from left to right, level by level).
For example:
Given binary tree [3,9,20,null,null,15,7],
3
/ \
9 20
/ \
15 7
return its level order traversal as:
[
[3],
[9,20],
[15,7]
]
Solution: BFS
class Solution(object):
def levelOrder(self, root):
"""
:type root: TreeNode
:rtype: List[List[int]]
"""
result = []
level = [root]
while level:
new_level = []
vals = []
for node in level:
if node:
vals.append(node.val)
new_level.append(node.left)
new_level.append(node.right)
if vals:
result.append(vals)
level = new_level
return result