二叉树先序遍历和中序遍历求后序遍历的代码

以下是二叉树先序遍历和中序遍历求后序遍历的代码：

class TreeNode:
    def __init__(self, val=0, left=None, right=None):
        self.val = val
        self.left = left
        self.right = right

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

def postorderTraversal(root):
    if not root:
        return []
    
    res = []
    stack = [(root, False)]
    
    while stack:
        node, visited = stack.pop()
        
        if not node:
            continue
        
        if visited:
            res.append(node.val)
        else:
            stack.append((node, True))
            stack.append((node.right, False))
            stack.append((node.left, False))
    
    return res

preorder = [1, 2, 4, 5, 3, 6, 7]
inorder = [4, 2, 5, 1, 6, 3, 7]

root = buildTree(preorder, inorder)
res = postorderTraversal(root)
print(res)

其中，`buildTree` 函数用于根据先序遍历和中序遍历构建二叉树，`postorderTraversal` 函数用于求二叉树的后序遍历。时间复杂度为 $O(n)$，空间复杂度为 $O(n)$，其中 $n$ 是二叉树的节点个数。