[LeetCode Python3] 103. Binary Tree Zigzag Level Order Traversal + 两种解法

最新推荐文章于 2021-02-05 11:10:39 发布

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本文介绍了一种二叉树的锯齿形层序遍历算法，通过两个栈来实现节点值的逐层交替反转输出，提供了两种不同的实现思路。

103. Binary Tree Zigzag Level Order Traversal

S1:

# V1 
class Solution:
    def zigzagLevelOrder(self, root: TreeNode) -> List[List[int]]:
        if not root:
            return None
        res, restmp = [], []
        stack0, stack1 = [root], []
        flag = True
        while stack0:
            tmp = stack0.pop()
            restmp.append(tmp.val)
            if flag:
                if tmp.left:
                    stack1.append(tmp.left)
                if tmp.right:
                    stack1.append(tmp.right)
            else:
                if tmp.right:
                    stack1.append(tmp.right)
                if tmp.left:
                    stack1.append(tmp.left)
            if not stack0:
                stack0 = stack1[:]
                stack1.clear()
                flag = not flag
                res.append(restmp[:])
                restmp.clear()
        return res

S2:

class Solution:
    def zigzagLevelOrder(self, root: TreeNode) -> List[List[int]]:
        if not root:
            return None
        res, restmp = [], []
        stack0, stack1 = [root], []
        flag = True
        while stack0:
            for tmp in stack0:
                restmp.append(tmp.val)
                if tmp.left:
                    stack1.append(tmp.left)
                if tmp.right:
                    stack1.append(tmp.right)
            stack0 = stack1[:]
            stack1.clear()
            if not flag:
                restmp.reverse()
            flag = not flag
            res.append(restmp[:])
            restmp.clear()
        return res