7-2 根据后序和中序遍历输出先序遍历 用python代码

以下是Python代码实现根据后序和中序遍历输出先序遍历的功能：

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

def buildTree(inorder, postorder):
    if not inorder or not postorder:
        return None
    root = TreeNode(postorder[-1])
    idx = inorder.index(root.val)
    root.left = buildTree(inorder[:idx], postorder[:idx])
    root.right = buildTree(inorder[idx+1:], postorder[idx:-1])
    return root

def preorderTraversal(root):
    res = []
    if not root:
        return res
    stack = [root]
    while stack:
        node = stack.pop()
        res.append(node.val)
        if node.right:
            stack.append(node.right)
        if node.left:
            stack.append(node.left)
    return res

inorder = [4, 2, 5, 1, 6, 3, 7]
postorder = [4, 5, 2, 6, 7, 3, 1]
root = buildTree(inorder, postorder)
preorder = preorderTraversal(root)
print(preorder)

输出结果为：[1, 2, 4, 5, 3, 6, 7]