LeetCode103 二叉树的锯齿形层序遍历

LeetCode103 二叉树的锯齿形层序遍历

使用两个栈进行模拟 + bfs

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    def zigzagLevelOrder(self, root: TreeNode) -> List[List[int]]:
        
        if root is None: return []

        ans, stack_odd, stack_even = [], [root], []

        while stack_odd or stack_even:

            if stack_odd:
                
                odd_ans = []
                while stack_odd:
                    cur = stack_odd.pop()
                    odd_ans.append(cur.val)
                    if cur.left: stack_even.append(cur.left)
                    if cur.right: stack_even.append(cur.right)
                ans.append(odd_ans)

            elif stack_even:

                even_ans = []
                while stack_even:
                    cur = stack_even.pop()
                    even_ans.append(cur.val)
                    if cur.right: stack_odd.append(cur.right)
                    if cur.left: stack_odd.append(cur.left)
                ans.append(even_ans)

        return ans