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Binary tree creation & traversal
2022-07-06 07:46:00 【Wang jijiya】
Hierarchy creation
Reference resources :Python --- Sequence establishment of binary tree
class TreeNode:
def __init__(self, val=0, left=None, right=None):
self.val = val
self.left = None
self.right = None
def creatTree(nodeList):
if nodeList[0] == None: return None
head = TreeNode(nodeList[0])
nodes = [head] # Used to store nodes in the tree , Every time a node is generated, it is placed in the list , Save the root node here .
j = 1 # Create variables j be used for nodeList The index of the element in the , For the initial 1. Because the first 0 Elements have created root nodes .
for node in nodes: # Take out one by one Nodes Nodes in the list , Create a left child node and a right child node
if node != None:
node.left = (TreeNode(nodeList[j])) if nodeList[j] != None else None
nodes.append(node.left) # Add the new node Nodes Array , Make it for In the loop, you can continue to add child nodes
j += 1
if j == len(nodeList): # If the nodeList Equal values indicate that all nodes have been added , Go straight back to head The root node completes the establishment of the tree
return head
node.right = (TreeNode(nodeList[j])) if nodeList[j] != None else None
j += 1
nodes.append(node.right)
if j == len(nodeList):
return head
a = [1,2,3,4,None,6,7]
a = creatTree(a)
# Use : Return the longest path of binary tree ,Leecode 124
class Solution:
def __init__(self):
self.maxSum = float("-inf")
def maxPathSum(self, root: TreeNode) -> int:
def maxGain(node):
if not node:
return 0
leftGain = max(maxGain(node.left), 0)
rightGain = max(maxGain(node.right), 0)
priceNewpath = node.val + leftGain + rightGain
self.maxSum = max(self.maxSum, priceNewpath)
return node.val + max(leftGain, rightGain)
maxGain(root)
return self.maxSum
s = Solution()
s.maxPathSum(a)
Continue......
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