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python二叉树常用算法总结

目录

  • 1.1 二叉树的初始化
  • 1.2 创建一个二叉树
  • 1.3 前序遍历
  • 1.4 中序遍历
  • 1.5 后序遍历
  • 1.6 层序遍历
  • 1.7 计算节点数
  • 1.8 计算树的深度
  • 1.9 计算树的叶子树
  • 1.10 获取第K层节点数
  • 1.11 判断两颗二叉树是否相同
  • 1.12 二叉树的镜像
  • 1.13 找最低公共祖先节点
  • 1.14 获取两个节点的距离
  • 1.15 找一个节点的所有祖宗节点

1.1 二叉树的初始化
#initial of BinaryTreeclass BinaryTree:def __init__(self,rootObj):self.val = rootObjself.left = Noneself.right = Nonedef insertLeft(self,newNode):if self.left == None:self.left = BinaryTree(newNode)else:t = BinaryTree(newNode)t.left = self.leftself.left = tdef insertRight(self,newNode):if self.right == None:self.right = BinaryTree(newNode)else:t = BinaryTree(newNode)t.right = self.rightself.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# 711#3 4 5 6#1 3 2 4root = 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:returnstack =[]print(node.val)stack.append(node)node = node.leftwhile stack!=[] or node:while node:print(node.val)stack.append(node)node = node.leftnode = stack[-1].rightstack.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 Nonestack = []stack.append(node)node = node.leftwhile stack!=[] or node:while node:stack.append(node)node = node.leftprint(stack[-1].val)node = stack[-1].rightstack.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:returnstack =[]stack.append(node)pre = Nonewhile 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 = nodestack.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:returnstack = []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 0return self.CountNode(root.left) + self.CountNode(root.right) + 1#非递归版本def CountNodeNotRev(self, root):if root == None:return 0stack = []stack.append(root)index = 0while index

1.8 计算树的深度
def getTreeDepth(self, root):if root == None:return 0left = self.getTreeDepth(root.left) + 1right = self.getTreeDepth(root.right) + 1return left if left>right else right


1.9 计算树的叶子树
def countLeaves(self, root):if root == None:return 0if root.left==None and root.right==None:return 1return 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 0if K == 1: return 1return 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 Trueelif root1 ==None or root2 == None: return Falsereturn 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: returntmp = root.leftroot.left = root.rightroot.right = tmpself.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: returnif root == node1 or root == node2: return rootleft = self.findLCA(root.left, node1, node2)right = self.findLCA(root.right, node1, node2)if left and right:return rootreturn 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+level2def FindLevel(self, node, target):if node == None: return -1if node == target: return 0level = self.FindLevel(node.left, target)if level == -1: level = self.FindLevel(node.right, target)if level != -1: return level + 1return -1


1.15 找一个节点的所有祖宗节点
def findAllAncestor(self, root, target):if root == None: return Falseif root == target: return Trueif self.findAllAncestor(root.left, target) or self.findAllAncestor(root.right, target):print(root.val)return Truereturn False

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