def build1(inorder, postorder):
if not inorder:
return None
elif len(inorder) == 1:
return TreeNode(inorder[0])
else:
postorder_root_val = postorder[-1]
root = TreeNode(postorder_root_val)
for i in range(len(inorder)):
if postorder_root_val == inorder[i]:
inorder_root_index = i
break
if inorder_root_index == 0:
root.left = None
root.right = build1(inorder[1:], postorder[:-1])
elif inorder_root_index == len(inorder) - 1:
root.left = build1(inorder[:-1], postorder[:-1])
root.right = None
else:
root.left = build1(inorder[:inorder_root_index],
postorder[:inorder_root_index])
root.right = build1(inorder[inorder_root_index + 1:],
postorder[inorder_root_index:-1])
return root
def deserialize_tree(s):
if not s:
return
val = s.pop(0)
root = None
if val != 'null':
root = TreeNode(val)
root.left = deserialize_tree(s)
root.right = deserialize_tree(s)
return root
def build1(preorder, inorder):
if not preorder:
return None
if len(preorder) <= 1:
return TreeNode(preorder[0])
root_node = preorder[0]
root = TreeNode(root_node)
for i in range(len(inorder)):
if root_node == inorder[i]:
inorder_root_node_index = i
break
root.left = build1(preorder[1:inorder_root_node_index + 1],
inorder[:inorder_root_node_index])
root.right = build1(preorder[inorder_root_node_index + 1:],
inorder[inorder_root_node_index + 1:])
return root
def before_middle_construct_tree(before_seq, middle_seq):
"""
根据二叉树的前序遍历和中序遍历重建二叉树
:param before_seq: List[int]
:param middle_seq: List[int]
:return: TreeNode
"""
if len(before_seq) == 0 or len(middle_seq) == 0:
return
root_node = TreeNode(before_seq[0])
root_index = middle_seq.index(root_node.val)
left_node = before_middle_construct_tree(before_seq[1:root_index + 1],
middle_seq[:root_index])
right_node = before_middle_construct_tree(before_seq[root_index + 1:],
middle_seq[root_index + 1:])
root_node.left = left_node
root_node.right = right_node
return root_node
