标签：取反 leetcode and tac etc nbsp tco node direct
Given a binary tree, return the zigzag level order traversal of its nodes‘ values. (ie, from left to right, then right to left for the next level and alternate between).
For example:
Given binary tree [3,9,20,null,null,15,7],
3
/ 9 20
/ 15 7
return its zigzag level order traversal as:
[ [3], [20,9], [15,7] ]
思路类似： level order Traversal，唯一的区别在于对于第一层，Push child进入stack的顺序是left then right。而第二层是right then left。用一个boolean dicrect 来控制这个方向，每一层取反一次。
1 class Solution(object): 2 def zigzagLevelOrder(self, root): 3 """ 4 :type root: TreeNode 5 :rtype: List[List[int]] 6 """ 7 stack1 = [] 8 stack2 = [] 9 stack1.append(root) 10 direct = True 11 ans = [] 12 while stack1: 13 self.helper(direct, ans, stack1, stack2) 14 stack1, stack2 = stack2, [] 15 direct = not direct 16 return ans[:-1] 17 18 19 def helper(self, direct, ans, stack1, stack2): 20 line = [] 21 while stack1: 22 cur = stack1.pop() 23 if cur != None: 24 line.append(cur.val) 25 if direct == True: 26 stack2.append(cur.left) 27 stack2.append(cur.right) 28 else: 29 stack2.append(cur.right) 30 stack2.append(cur.left) 31 ans.append(line)
Leetcode 103. Binary Tree Zigzag Level Order Traversal
标签：取反 leetcode and tac etc nbsp tco node direct
原文地址：http://www.cnblogs.com/lettuan/p/6348107.html
