编写程序实现根据用户输入二叉树的先序序列建立一棵二叉树，并实现对此二叉树的先序中序和后序遍历

好的，下面是 Python 语言的实现代码：

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

def build_tree(preorder, inorder):
    if not preorder:
        return None
    root_val = preorder[0]
    root = TreeNode(root_val)
    idx = inorder.index(root_val)
    root.left = build_tree(preorder[1:idx+1], inorder[:idx])
    root.right = build_tree(preorder[idx+1:], inorder[idx+1:])
    return root

def preorder_traversal(root):
    if not root:
        return []
    res = []
    res.append(root.val)
    res += preorder_traversal(root.left)
    res += preorder_traversal(root.right)
    return res

def inorder_traversal(root):
    if not root:
        return []
    res = []
    res += inorder_traversal(root.left)
    res.append(root.val)
    res += inorder_traversal(root.right)
    return res

def postorder_traversal(root):
    if not root:
        return []
    res = []
    res += postorder_traversal(root.left)
    res += postorder_traversal(root.right)
    res.append(root.val)
    return res

if __name__ == '__main__':
    preorder = list(map(int, input().split()))
    inorder = list(map(int, input().split()))
    root = build_tree(preorder, inorder)
    print(' '.join(map(str, preorder_traversal(root))))
    print(' '.join(map(str, inorder_traversal(root))))
    print(' '.join(map(str, postorder_traversal(root))))

输入格式为二叉树的先序遍历和中序遍历，输出格式为先序遍历、中序遍历和后序遍历的结果，均以空格分隔。