題目描述
請實現一個函式按照之字形列印二叉樹，即第一行按照從左到右的順序列印，第二層按照從右至左的順序列印，第三行按照從左到右的順序列印，其他行以此類推。

在上一篇部落格中：層次遍歷，每一層在一行輸出中，只需要將奇數行的result反轉一下就行了
另外一種方法就是，需要反轉佇列的結果，想到就是用到棧
需要用到兩個棧，依次入棧，出棧，輸出就行
如果列印是奇數層，先儲存左節點再儲存右節點到棧，如果是偶數，則先儲存右再儲存左

class TreeNode:
    def __init__(self, x):
        self.val = x
        self.
 
left = None
        self.right = None
class Solution:
    def Print(self, pRoot):
        # write code here
        list = []  #佇列
        result = []  #每一層的結果
        results = []  #儲存result的list
        nextLevel = 0
        toBeList = 1   #這層還需要加入result的元素個數
        if pRoot == None:
            return
 
 list
        list.append(pRoot)
        while list != []:
            treeNode = list.pop(0)
            toBeList -= 1
            result.append(treeNode.val)
            if treeNode.left:
                nextLevel += 1
                list.append(treeNode.left)
            if treeNode.right:
                nextLevel +=
 
 1
                list.append(treeNode.right)
            if toBeList == 0:
                results.append(result)
                result = []
                toBeList = nextLevel
                nextLevel = 0
        for i, result in enumerate(results):
            if i & 0x1 == 1:
                result.reverse()
        return results

結果

root = TreeNode(1)
root.left = TreeNode(2)
root.right = TreeNode(3)
root.left.left = TreeNode(4)
root.right.left = TreeNode(5)
root.right.right = TreeNode(6)
results = Solution().Print(root)
for i in results:
    print(i)
>>>
[1]
[3, 2]
[4, 5, 6]