# Leetcode: Binary Tree Level Order Traversal

Binary Tree Level Order Traversal

Similar Problems:

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]
]
```

Github: code.dennyzhang.com

Credits To: leetcode.com

Leave me comments, if you have better ways to solve.

```## Blog link: https://code.dennyzhang.com/binary-tree-level-order-traversal
## Baisc Idea: BFS
## Complexity: Time O(n), Space O(n)
# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution(object):
def levelOrder(self, root):
"""
:type root: TreeNode
:rtype: List[List[int]]
"""

if root is None: return []
res = []
queue = collections.deque()
queue.append(root)
while len(queue) != 0:
level_elements = []
for i in xrange(len(queue)):
element = queue.popleft()
level_elements.append(element.val)
if element.left:
queue.append(element.left)
if element.right:
queue.append(element.right)
res.append(level_elements)
return res
```

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