定义二叉树:
class TreeNode:
def __init__(self, x):
self.val = x
self.left = None
self.right = None
构建二叉树:
# 返回构造的TreeNode根节点
def reConstructBinaryTree(self, pre, tin):
if not pre or not tin:
return None
root = TreeNode(pre[0])#根节点
# 判断输入的两个序列是不是匹配
if set(pre) != set(tin):
return None
i = tin.index(root.val) # i == 3
root.left = self.reConstructBinaryTree(pre[1:i+1],tin[:i]) # 列表:左闭右开
root.right = self.reConstructBinaryTree(pre[i+1:],tin[i+1:])
return root
BFS:
def BFS(self, root): # 宽度优先遍历BFS
array = []
result = []
if root == None:
return result
array.append(root)
while array:
newNode = array.pop(0) # 根结点
result.append(newNode.val)
if newNode.left != None:
array.append(newNode.left)
if newNode.right != None:
array.append(newNode.right)
return result
先序遍历:
1.递归版本:
def pre_traversal(self):
ret = []
def traversal(head):
if not head:
return
ret.append(head.val)
traversal(head.left)
traversal(head.right)
traversal(self.root)
return ret
2.非递归版本:
# 先序打印二叉树(非递归)
def preOrderTravese(node):
stack = [node]
while len(stack) > 0:
print(node.val)
if node.right is not None:
stack.append(node.right)
if node.left is not None:
stack.append(node.left)
node = stack.pop()
中序遍历:
1.递归版本
def in_traversal(self):
ret = []
def traversal(head):
if not head:
return
traversal(head.left)
ret.append(head.val)
traversal(head.right)
traversal(self.root)
return ret
2.非递归版本
# 中序打印二叉树(非递归)
def inOrderTraverse(node):
stack = []
pos = node
while pos is not None or len(stack) > 0:
if pos is not None:
stack.append(pos)
pos = pos.left
else:
pos = stack.pop()
print(pos.val)
pos = pos.right
后序遍历:
1.递归版本
def post_traversal(self):
ret = []
def traversal(head):
if not head:
return
traversal(head.left)
traversal(head.right)
ret.append(head.val)
traversal(self.root)
return ret
2.非递归版本
# 后序打印二叉树(非递归)
# 使用两个栈结构
# 第一个栈进栈顺序:左节点->右节点->跟节点(?应该是根-左-右?根结点先进栈再出栈,然后左右子节点入栈?)
# 第一个栈弹出顺序: 跟节点->右节点->左节点(先序遍历栈弹出顺序:跟->左->右)
# 第二个栈存储为第一个栈的每个弹出依次进栈
# 最后第二个栈依次出栈
def postOrderTraverse(node):
stack = [node]
stack2 = []
while len(stack) > 0:
node = stack.pop()
stack2.append(node)
if node.left is not None:
stack.append(node.left)
if node.right is not None:
stack.append(node.right)
while len(stack2) > 0:
print(stack2.pop().val)
求二叉树最大深度:
# 二叉树的最大深度
def bTreeDepth(node):
if node is None:
return 0
print '当前节点',node.data
ldepth = bTreeDepth(node.left)
print ' 节点', node.data,'的左侧深度',ldepth
rdepth = bTreeDepth(node.right)
print ' 节点', node.data,'的右侧深度',rdepth
return max(ldepth, rdepth) + 1
求二叉树节点个数:
# 求二叉树节点个数
def treeNodenums(node):
if node is None:
return 0
print "当前节点",node.data
nums = treeNodenums(node.left)
print ' ', node.data, '的左节点数', nums
right = treeNodenums(node.right)
print ' ', node.data, '的右节点数', right
nums = nums + right
print ' ', node.data, '的左右节点总数', nums
return nums + 1 # 返回上一级加上父节点
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