2020数据结构小学期（三）——由遍历序列恢复二叉树算法

3、由遍历序列恢复二叉树

输入：遍历序列

功能要求：输出二叉树形态或输出二叉树的三种遍历序列

源码：

class TreeNode():
    def __init__(self, val, left=None, right=None):
        self.val = val
        self.left = left
        self.right = right


def post_print(root):
    if root:
        post_print(root.left)
        post_print(root.right)
        print(root.val, end=" ")


def restore_tree(pre_order, in_order):
    if len(pre_order) == 0:
        return None
    elif len(in_order) == 1:
        return TreeNode(in_order[0])
    else:
        root = pre_order[0]
        depth = in_order.index(root)
        temp = TreeNode(root)
        temp.left = restore_tree(pre_order[1:depth + 1], in_order[:depth])
        temp.right = restore_tree(pre_order[depth + 1:], in_order[depth + 1:])
    return temp


if __name__ == '__main__':
    pre_str = input("请输入先序遍历序列：")
    in_str = input("请输入中序遍历序列：")
    # pre_order = ['A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I']
    # in_order = ['B', 'C', 'A', 'E', 'D', 'G', 'H', 'F', 'I']
    pre_order = []
    in_order = []
    for char in pre_str:
        pre_order.append(char)
    for char in in_str:
        in_order.append(char)
    temp = restore_tree(pre_order, in_order)
    print("先序遍历：")
    for char in pre_order:
        print(char, end=" ")
    print()
    print("中序遍历：")
    for char in in_order:
        print(char, end=" ")
    print()
    print("后序遍历：")
    post_print(temp)