def buildTree_v2(preorder, inorder):
if inorder:
ind = inorder.index(preorder.pop(0))
root = TreeNode(inorder[ind])
root.left = buildTree(preorder, inorder[0:ind])
root.right = buildTree(preorder, inorder[ind+1:])
return root
def build(inorder, postorder, inStart, inEnd, postStart, postEnd):
# print(inStart, inEnd, postStart, postEnd)
if inEnd - inStart == 0:
return None
if inEnd - inStart == 1:
return TreeNode(postorder[postStart])
root = TreeNode(postorder[postEnd - 1])
left_in_set = set()
pointer = inStart
while inorder[pointer] != root.val:
left_in_set.add(inorder[pointer])
pointer += 1
leftInEnd = pointer
rightInStart = pointer + 1
pointer = postStart
while postorder[pointer] in left_in_set:
pointer += 1
leftPosEnd = pointer
rightPosStart = pointer
root.left = build(inorder, postorder, inStart, leftInEnd, postStart, leftPosEnd)
root.right = build(inorder, postorder, rightInStart, inEnd, rightPosStart, postEnd - 1)
return root
def recursive(startN, endN, d):
"""
:param startN:
:param endN:
:param result:
:return:
"""
if (startN, endN) in d:
return d[(startN, endN)]
if endN - startN < 0:
d[(startN, endN)] = [None]
return d[(startN, endN)]
if endN - startN == 0:
d[(startN, endN)] = [TreeNode(startN)]
return d[(startN, endN)]
ans = []
for i in range(startN, endN + 1):
ansL = recursive(startN, i - 1, d)
ansR = recursive(i + 1, endN, d)
for nl in ansL:
for nr in ansR:
node = TreeNode(i)
node.left = nl
node.right = nr
ans.append(node)
return ans
def buildTree(inorder, postorder):
if inorder:
ind = inorder.index(postorder.pop())
root = TreeNode(inorder[ind])
root.right = buildTree(inorder[ind+1:], postorder)
root.left = buildTree(inorder[:ind], postorder)
return root
return None
def sortedArrayToBST(nums):
if len(nums) == 0:
return None
if len(nums) == 1:
return TreeNode(nums[0])
mid = len(nums) // 2
root = TreeNode(nums[mid])
root.left = sortedArrayToBST(nums[0:mid])
root.right = sortedArrayToBST(nums[mid + 1 :])
return root
def buildTree(preorder, inorder):
"""
:param preorder:
:param inorder:
:return:
"""
if len(preorder) != len(inorder):
raise Exception('len(preorder) != len(inorder)')
if not preorder:
return None
if len(preorder) == 1:
return TreeNode(preorder[0])
root = TreeNode(preorder[0])
left_pre = []
left_in = []
right_pre = []
right_in = []
pointer = 0
while inorder[pointer] != root.val:
left_in.append(inorder[pointer])
pointer += 1
pointer += 1
while pointer < len(inorder):
right_in.append(inorder[pointer])
pointer += 1
left_set = set(left_in)
pointer = 1
while pointer < len(preorder):
e = preorder[pointer]
pointer += 1
if e in left_set:
left_pre.append(e)
else:
right_pre.append(e)
root.left = buildTree(left_pre, left_in)
root.right = buildTree(right_pre, right_in)
return root
