python二叉树常用算法总结

1.1 二叉树的初始化

#initial of BinaryTree
class BinaryTree:
   def __init__(self,rootObj):
       self.val = rootObj
       self.left = None
       self.right = None

def insertLeft(self,newNode):
       if self.left == None:
           self.left = BinaryTree(newNode)
       else:
           t = BinaryTree(newNode)
           t.left = self.left
           self.left = t

def insertRight(self,newNode):
       if self.right == None:
           self.right = BinaryTree(newNode)
       else:
           t = BinaryTree(newNode)
           t.right = self.right
           self.right = t

1.2 创建一个二叉树

#create a BinaryTree [18,7,11,3,4,5,6,#,#,#,#,1,3,2,4]
#  18
# 7  11
#3 4 5 6
#   1 3 2 4

root = BinaryTree(18)
root.left = BinaryTree(7)
root.right = BinaryTree(11)
root.left.left = BinaryTree(3)
root.left.right = BinaryTree(4)
root.right.left = BinaryTree(5)
root.right.right = BinaryTree(6)
root.right.left.left = BinaryTree(1)
root.right.left.right = BinaryTree(3)
root.right.right.left = BinaryTree(2)
root.right.right.right = BinaryTree(4)

1.3 前序遍历

#递归版本
def PreOrder(self, node):
   if node:
       print(node.val)
       self.PreOrder(node.left)
       self.PreOrder(node.right)
#循环版本
def PreOrderLoop(self, node):
   if node == None:
       return
   stack =[]
   print(node.val)
   stack.append(node)
   node = node.left
   while stack!=[] or node:
       while node:
           print(node.val)
           stack.append(node)
           node = node.left
       node = stack[-1].right
       stack.pop()

#ouput: 18 7 3 4 11 5 1 3 6 2 4

1.4 中序遍历

#递归版本
def InOrder(self, node):
   if node:
       self.InOrder(node.left)
       print(node.val)
       self.InOrder(node.right)
#循环版本
def InOrderLoop(self, node):
   if node == None:
       return None
   stack = []
   stack.append(node)
   node = node.left
   while stack!=[] or node:
       while node:
           stack.append(node)
           node = node.left
       print(stack[-1].val)
       node = stack[-1].right
       stack.pop()
#output：3 7 4 18 1 5 3 11 2 6 4

1.5 后序遍历

#递归
def PostOrder(self, node):
   if node:
       self.PostOrder(node.left)
       self.PostOrder(node.right)
       print(node.val)
#非递归
def PostOrderLoop(self, node):
   if node == None:
       return
   stack =[]
   stack.append(node)
   pre = None
   while stack!=[]:
       node = stack[-1]
       if ((node.left==None and node.right==None) or
               (pre and (pre == node.left or pre ==node.right))):
           print(node.val)
           pre = node
           stack.pop()
       else:
           if node.right:
               stack.append(node.right)
           if node.left:
               stack.append(node.left)
#output:3 4 7 1 3 5 2 4 6 11 18

1.6 层序遍历

def LevelOrder(self, node):
   if node == None:
       return
   stack = []
   stack.append(node)
   while stack!=[]:
       node = stack[0]
       if node.left:
           stack.append(node.left)
       if node.right:
           stack.append(node.right)
       print(node.val)
       stack.pop(0)
output: 18 7 11 3 4 5 6 1 3 2 4

1.7 计算节点数

#递归版本
def CountNode(self, root):
   if root == None:
       return 0
   return self.CountNode(root.left) + self.CountNode(root.right) + 1
#非递归版本
def CountNodeNotRev(self, root):
   if root == None:
       return 0
   stack = []
   stack.append(root)
   index = 0
   while index<len(stack):
       if stack[index].left:
           stack.append(stack[index].left)
       if stack[index].right:
           stack.append(stack[index].right)
       index += 1
   print(len(stack))
output: 11

1.8 计算树的深度

def getTreeDepth(self, root):
   if root == None:
       return 0
   left = self.getTreeDepth(root.left) + 1
   right = self.getTreeDepth(root.right) + 1
   return left if left>right else right

1.9 计算树的叶子树

def countLeaves(self, root):
   if root == None:
       return 0
   if root.left==None and root.right==None:
       return 1
   return self.countLeaves(root.left)+self.countLeaves(root.right)

1.10 获取第K层节点数

def getKLevel(self, root, K):
   if root == None: return 0
   if K == 1: return 1
   return self.getKLevel(root.left, K-1)+self.getKLevel(root.right, K-1)

1.11 判断两颗二叉树是否相同

def StrucCmp(self, root1, root2):
   if root1 == None and root2 == None: return True
   elif root1 ==None or root2 == None: return False
   return self.StrucCmp(root1.left, root2.left) and self.StrucCmp(root1.right, root2.right)

1.12 二叉树的镜像

def Mirror(self, root):
   if root == None: return
   tmp = root.left
   root.left = root.right
   root.right = tmp
   self.Mirror(root.left)
   self.Mirror(root.right)

1.13 找最低公共祖先节点

def findLCA(self, root, node1, node2):
   if root == None: return
   if root == node1 or root == node2: return root
   left = self.findLCA(root.left, node1, node2)
   right = self.findLCA(root.right, node1, node2)
   if left and right:
       return root
   return left if left else right

1.14 获取两个节点的距离

def getDist(self, root, node1, node2):
   lca = self.findLCA(root, node1, node2) #找最低公共祖宗节点
   level1 = self.FindLevel(lca, node1) #祖节点到两个节点的距离
   level2 = self.FindLevel(lca, node2)
   return level1+level2
def FindLevel(self, node, target):
   if node == None: return -1
   if node == target: return 0
   level = self.FindLevel(node.left, target)
   if level == -1: level = self.FindLevel(node.right, target)
   if level != -1: return level + 1
   return -1

1.15 找一个节点的所有祖宗节点

def findAllAncestor(self, root, target):
   if root == None: return False
   if root == target: return True
   if self.findAllAncestor(root.left, target) or self.findAllAncestor(root.right, target):
       print(root.val)
       return True
   return False

来源：https://bbs.huaweicloud.com/blogs/254847