class Solution:
# inplace - swap left and right child and resursive invert left and right
def invertTree(self, root):
"""
:type root: TreeNode
:rtype: TreeNode
"""
if root:
root.left, root.right = root.right, root.left
self.invertTree(root.left)
self.invertTree(root.right)
return root
# inplace - one liner
def invertTree2(self, root):
invert = self.invertTree2
if root:
root.left, root.right = invert(root.right), invert(root.left)
return root
# import
import sys, os
sys.path.insert(0, os.path.abspath((os.pardir + os.sep) * 2 + 'mylib'))
from BinaryTreeTraversalGenerator import TreeNode, build_tree_from_list, serialize_tree_to_array
# test
root = build_tree_from_list([4, 2, 7, 1, 3, 6, 9])
print(serialize_tree_to_array(Solution().invertTree(root)))
root = build_tree_from_list([4, 2, 7, 1, 3, 6, 9])
print(serialize_tree_to_array(Solution().invertTree2(root)))
# self.right = None
class Solution:
# DP topdown resursive with memo
def generateTrees(self, n):
def generate(start, end):
if start > end:
return [None]
if (start, end) in memo:
return memo[(start, end)]
res = []
for i in range(start, end+1):
for left in generate(start, i-1):
for right in generate(i+1, end):
node = TreeNode(i)
node.left, node.right = left, right
res.append(node)
memo[(start, end)] = res
return res
if not n:
return []
memo = {}
return generate(1, n)
# import
import sys, os
sys.path.insert(0, os.path.abspath((os.pardir + os.sep) * 2 + 'mylib'))
from BinaryTreeTraversalGenerator import TreeNode, serialize_tree_to_array
# test
for root in Solution().generateTrees(3):
print(serialize_tree_to_array(root))
root.right = build(inorder_ix + 1, inorder_end)
return root
inorder_dict = {v: i for i, v in enumerate(inorder)}
self.preorder_ix = 0 # the cur index of preorder - pass by reference
return build(0, len(inorder)) # NOT len-1!!
# import
import sys, os
sys.path.insert(0, os.path.abspath((os.pardir + os.sep) * 2 + 'mylib'))
from BinaryTreeTraversalGenerator import TreeNode, serialize_tree_to_array
inorder = [9, 5, 1, 7, 2, 12, 8, 4, 3, 11]
preorder = [8, 5, 9, 7, 1, 12, 2, 4, 11, 3]
'''
8
/ \
5 4
/ \ \
9 7 11
/ \ /
1 12 3
/
2
'''
# test
print(serialize_tree_to_array(Solution().buildTree(preorder[:], inorder)))
print(serialize_tree_to_array(Solution().buildTree2(preorder, inorder)))
root.right = build(inorder_ix + 1, inorder_end)
root.left = build(inorder_start, inorder_ix)
return root
inorder_dict = {v: i for i, v in enumerate(inorder)}
# the cur index of postorder - pass by reference
self.postorder_ix = len(postorder) - 1
return build(0, len(inorder)) # NOT len-1!!
# import
import sys, os
sys.path.insert(0, os.path.abspath((os.pardir + os.sep) * 2 + 'mylib'))
from BinaryTreeTraversalGenerator import TreeNode, serialize_tree_to_array
inorder = [9, 5, 1, 7, 2, 12, 8, 4, 3, 11]
postorder = [9, 1, 2, 12, 7, 5, 3, 11, 4, 8]
'''
8
/ \
5 4
/ \ \
9 7 11
/ \ /
1 12 3
/
2
'''
# test
print(serialize_tree_to_array(Solution().buildTree(inorder, postorder[:])))
print(serialize_tree_to_array(Solution().buildTree2(inorder, postorder)))
/ \
1 3
'''
# Definition for a binary tree node.
# class TreeNode(object):
# def __init__(self, x):
# self.val = x
# self.left = None
# self.right = None
class Solution:
def sortedArrayToBST(self, nums):
"""
:type nums: List[int]
:rtype: TreeNode
"""
if not nums:
return None
mid = len(nums) // 2
root = TreeNode(nums[mid])
root.left = self.sortedArrayToBST(nums[:mid])
root.right = self.sortedArrayToBST(nums[mid+1:])
return root
# import
import sys, os
sys.path.insert(0, os.path.abspath((os.pardir + os.sep) * 2 + 'mylib'))
from BinaryTreeTraversalGenerator import TreeNode, serialize_tree_to_array
# test
print(serialize_tree_to_array(Solution().sortedArrayToBST([1,2,3])))
print(serialize_tree_to_array(Solution().sortedArrayToBST([1,2,3,4,5,6,7])))