def insertIntoBST(self, root: TreeNode, val: int) -> TreeNode:
if root == None:
return TreeNode(val)
elif val < root.val:
root.left = self.insertIntoBST(root.left, val)
else:
root.right = self.insertIntoBST(root.right, val)
return root
def buildTree(self, preorder: List[int], inorder: List[int]) -> TreeNode:
if not preorder:
return None
root = TreeNode(preorder[0])
idx = inorder.index(preorder[0])
root.left = self.buildTree(preorder[1:1 + idx], inorder[0:idx])
root.right = self.buildTree(preorder[1 + idx:], inorder[idx + 1:])
return root
def helper(arr):
if not arr:
return None
mid = len(arr) // 2
rtn = TreeNode(arr[mid])
rtn.left = helper(arr[:mid])
rtn.right = helper(arr[mid + 1:])
return rtn
def buildTree(self, inorder: List[int], postorder: List[int]) -> TreeNode:
if not inorder:
return None
rtn = TreeNode(postorder[-1])
idx = inorder.index(postorder[-1])
rtn.left = self.buildTree(inorder[:idx], postorder[:idx])
rtn.right = self.buildTree(inorder[idx + 1:],
postorder[idx:len(postorder) - 1])
return rtn
def mergeTrees(self, root1: TreeNode, root2: TreeNode) -> TreeNode:
if not root1 and not root2:
return None
new_tree = TreeNode(0)
n1 = root1 if root1 else TreeNode(0)
n2 = root2 if root2 else TreeNode(0)
new_tree.val = n1.val + n2.val
new_tree.left = self.mergeTrees(n1.left, n2.left)
new_tree.right = self.mergeTrees(n1.right, n2.right)
return new_tree
def trimBST(self, root: TreeNode, low: int, high: int) -> TreeNode:
if root:
if root.val < low:
root = self.trimBST(root.right, low, high)
elif root.val > high:
root = self.trimBST(root.left, low, high)
else:
root.left = self.trimBST(root.left, low, high)
root.right = self.trimBST(root.right, low, high)
return root
def rec(self, root, sum):
if root is None:
return (sum, None)
total, r = self.rec(root.right, sum)
new_root = TreeNode(root.val + total)
new_total, l = self.rec(root.left, new_root.val)
new_root.left = l
new_root.right = r
return (new_total, new_root)
def deleteNode(self, root: TreeNode, key: int) -> TreeNode:
if not root:
return root
if root.val == key:
if not root.left:
return root.right
elif not root.right:
return root.left
else:
# Find successor
succ = root.right
while succ and succ.left:
succ = succ.left
root.val = succ.val
root.right = self.deleteNode(root.right, succ.val)
elif key < root.val:
root.left = self.deleteNode(root.left, key)
else:
root.right = self.deleteNode(root.right, key)
return root
def expan(node: TreeNode):
if node.left is None and node.right is None:
return node
if node.left is None:
return expan(node.right)
if node.right is None:
ltail = expan(node.left)
node.right = node.left
node.left = None
return ltail
ltail = expan(node.left)
l = node.left
r = node.right
node.left = None
node.right = l
ltail.right = r
rtail = expan(r)
return rtail
def helper(pre_tran, post_tran):
if not pre_tran:
return None
ret = TreeNode(pre_tran[0])
if len(pre_tran) > 1:
right_root = post_tran[-2]
right_idx = pre_tran.index(right_root)
ret.left = helper(pre_tran[1:right_idx],
post_tran[:right_idx - 1])
ret.right = helper(pre_tran[right_idx:],
post_tran[right_idx - 1:len(post_tran) - 1])
return ret
def helper(k):
if k not in mem:
rtn = []
for i in range(1, k - 1, 2):
for left in helper(i):
for right in helper(k - i - 1):
cur = TreeNode()
cur.left = left
cur.right = right
rtn.append(cur)
mem[k] = rtn
return mem[k]
def build_tree(start, end):
if start > end:
return [None]
rtn = []
for cur_val in range(start, end + 1):
cur_left = build_tree(start, cur_val - 1)
cur_right = build_tree(cur_val + 1, end)
for left in cur_left:
for right in cur_right:
node = TreeNode(cur_val)
node.left = left
node.right = right
rtn.append(node)
return rtn
def sortedListToBST(self, head: ListNode) -> TreeNode:
if not head:
return None
slow, fast = head, head
pre = None
while fast and fast.next:
pre = slow
slow = slow.next
fast = fast.next.next
if pre:
pre.next = None
rtn = TreeNode(slow.val)
rtn.left = self.sortedListToBST(head) if head != slow else None
rtn.right = self.sortedListToBST(slow.next)
return rtn
def deleteNode(self, root: TreeNode, key: int) -> TreeNode:
if not root:
return None
if root.val == key:
if not root.left:
return root.right
if not root.right:
return root.left
new_root = root.left
while new_root.right:
new_root = new_root.right
root.val, new_root.val = new_root.val, root.val
root.left = self.deleteNode(root.left, key)
elif root.val > key:
root.left = self.deleteNode(root.left, key)
else:
root.right = self.deleteNode(root.right, key)
return root
def mergeTrees(self, t1, t2):
"""
:type t1: TreeNode
:type t2: TreeNode
:rtype: TreeNode
"""
if t1 is None and t2 is None:
return None
root = TreeNode(0)
if t1:
root.val += t1.val
if t2:
root.val += t2.val
root.left = self.mergeTrees(t1.left if t1 else None, t2.left if t2 else None)
root.right = self.mergeTrees(t1.right if t1 else None, t2.right if t2 else None)
return root
def traverse(post_beg, post_end, in_beg, in_end):
if post_end <= post_beg:
return None
# Find the index of current root in inorder traversal list
idx = inorder_indices[postorder[post_end - 1]]
root = TreeNode(inorder[idx])
# The portion of left subtree in the inorder list is given by [in_beg : idx]
# The portion of right subtree in the inorder list is given by [idx + 1 : in_end]
# The lengths of left and right are given by (idx - in_beg) and (in_end - idx)
# Now we can obtain the portions of left and right subtree from the post order list:
# Left subtree in the postorder list: [post_beg : idx]
# Right subtree in the postorder list: [idx + 1 : in_end]
# Construct both subtrees recursively
root.left = traverse(post_beg, post_beg + idx - in_beg, in_beg,
idx)
root.right = traverse(post_end - in_end + idx, post_end - 1,
idx + 1, in_end)
return root
