102、Binary Tree Level Order Traversal

题目：

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,#,#,15,7},

    3   / \  9  20    /  \   15   7

return its level order traversal as:

[  [3],  [9,20],  [15,7]]

解题思路：

二叉树的层次遍历

# Definition for a binary tree node.# class TreeNode(object):#     def __init__(self, x):#         self.val = x#         self.left = None#         self.right = Noneclass Solution(object):    def levelOrder(self, root):        """        :type root: TreeNode        :rtype: List[List[int]]        """        def levtrav(q):            tmp = q[:]            for l in tmp:                x = q.pop(0)                if(x.left!=None):                    q.append(x.left)                if(x.right!=None):                    q.append(x.right)            return q                    res,queue = [],[]        if(root):            res.append([root.val])            queue.append(root)        while(len(queue)!=0):            tmp = []            for l in queue:                if(l.left!=None):                    tmp.append(l.left.val)                if(l.right!=None):                    tmp.append(l.right.val)            if(tmp!=[]):                res.append(tmp)            queue = levtrav(queue[:])        return res