Binary Tree Zigzag Level Order Traversal

 

# Definition for a  binary tree node
class TreeNode:
    def __init__(self, x):
        self.val = x
        self.left = None
        self.right = None

class Solution:
    # @param root, a tree node
    # @return a list of lists of integers
    def zigzagLevelOrder(self, root):
        res=[]
        nodes=[]
        nodes.append(root)
        order=1 #表示这一层显示的顺序

        while(nodes!=[]):
            level=[]  #存放这一层的val值
            for i in range(len(nodes)):
                if nodes[i]!=None:
                    level.append(nodes[i].val)
            if level!=[]:
                if order==1: # 顺序存放
                    res.append(level)
                else:  # 反序存放
                    antitone_level=[]
                    for j in range(len(level)):
                        antitone_level.append(level[len(level)-1-j])
                    res.append(antitone_level)
                order=order*(-1)

            temp=[]  #将这一层节点的叶节点存放在nodes中
            for i in range(len(nodes)):
                if nodes[i]!=None:
                    temp.append(nodes[i].left)
                    temp.append(nodes[i].right)
            nodes=temp

        print(res)
        return res

if __name__ == '__main__':
    root=TreeNode(3)
    l=TreeNode(9)
    r=TreeNode(20)
    rl=TreeNode(15)
    rr=TreeNode(7)
    root.left=l
    root.right=r
    r.left=rl
    r.right=rr

    s=Solution()
    s.zigzagLevelOrder(root)