class TreeNode(object): #定义二叉树类
    def init(self,val,left=None,right=None):
        self.val = val
        self.left = left
        self.right = right


class BinaryTree(object):
    def __init__(self,root=None):
    self.root = root

    def preScan(self,retList, node): #先序遍历：先跟、再左、后右
        if node != None:
            retList.append(node.val)
            self.preScan(retList, node.left)
            self.preScan(retList, node.right)
        return retList

    def midScan(self, retList, node): #中序遍历：先左、再跟、后右
        if node != None:
            self.midScan(retList, node.left)
            retList.append(node.val)
            self.midScan(retList, node.right)
        return retList

    def postScan(self, retList, node): #后序遍历：先左、再右、后跟
        if node != None:
            self.postScan(retList, node.left)
            self.postScan(retList, node.right)
            retList.append(node.val)
        return retList

if __name__ == "__main__":
    root = TreeNode(50)
    root.left = TreeNode(20,left=TreeNode(15),right=TreeNode(30,right=TreeNode(12)))
    root.right = TreeNode(60,right=TreeNode(70))
    bTree = BinaryTree(root)
    retList = bTree.preScan([],bTree.root)
    print(retList)
    retList2 = bTree.midScan([],bTree.root)
    print(retList2)
    retList3 = bTree.postScan([],bTree.root)
    print(retList3)