对于找工作的兄弟来说,构建二叉树和七种遍历方式肯定是要求能手写的,无需解释。
直接上代码吧,注释里什么都有:
class Node():
# 节点类
def __init__(self, data=-1):
self.data = data
self.left = None
self.right = None
class Tree():
# 树类
def __init__(self):
self.root = Node()
def add(self, data):
# 为树加入节点
node = Node(data)
if self.root.data == -1: # 如果树为空,就对根节点赋值
self.root = node
else:
myQueue = []
treeNode = self.root
myQueue.append(treeNode)
while myQueue: # 对已有的节点进行层次遍历
treeNode = myQueue.pop(0)
if not treeNode.left:
treeNode.left = node
return
elif not treeNode.right:
treeNode.right = node
return
else:
myQueue.append(treeNode.left)
myQueue.append(treeNode.right)
def pre_order_recursion(self, root): # 递归实现前序遍历
if not root:
return
print(root.data),
self.pre_order_recursion(root.left)
self.pre_order_recursion(root.right)
def pre_order_stack(self, root): # 堆栈实现前序遍历(非递归)
if not root:
return
myStack = []
node = root
while myStack or node:
while node: # 从根节点开始,一直寻找他的左子树
print(node.data),
myStack.append(node)
node = node.left
node = myStack.pop() # while结束表示当前节点node为空,即前一个节点没有左子树了
node = node.right # 开始查看它的右子树
def in_order_recursion(self, root): # 递归实现中序遍历
if not root:
return
self.in_order_recursion(root.left)
print(root.data),
self.in_order_recursion(root.right)
def in_order_stack(self, root): # 堆栈实现中序遍历(非递归)
if not root:
return
myStack = []
node = root
while myStack or node: # 从根节点开始,一直寻找它的左子树
while node:
myStack.append(node)
node = node.left
node = myStack.pop()
print(node.data),
node = node.right
def post_order_recursion(self, root): # 递归实现后序遍历
if not root:
return
self.post_order_recursion(root.left)
self.post_order_recursion(root.right)
print(root.data),
def post_order_stack(self, root): # 堆栈实现后序遍历(非递归)
# 先遍历根节点,再遍历右子树,最后是左子树,这样就可以转化为和先序遍历一个类型了,最后只把遍历结果逆序输出就OK了。
if not root:
return
myStack1 = []
# stack2是为了逆序输出
myStack2 = []
node = root
while myStack1 or node:
while node:
myStack2.append(node)
myStack1.append(node)
node = node.right
node = myStack1.pop()
node = node.left
while myStack2:
print(myStack2.pop().data),
def level_order_queue(self, root): # 队列实现层次遍历(非递归)
if not root:
return
myQueue = []
node = root
myQueue.append(node)
while myQueue:
node = myQueue.pop(0)
print(node.data),
if node.left:
myQueue.append(node.left)
if node.right:
myQueue.append(node.right)
if __name__ == '__main__':
# 主函数
datas = [1,2, 3,4]
tree = Tree() # 新建一个树对象
for data in datas:
tree.add(data) # 逐个加入树的节点
print('递归实现前序遍历:')
tree.pre_order_recursion(tree.root)
print('\n堆栈实现前序遍历')
tree.pre_order_stack(tree.root)
print("\n\n递归实现中序遍历:")
tree.in_order_recursion(tree.root)
print("\n堆栈实现中序遍历:")
tree.in_order_stack(tree.root)
print('\n\n递归实现后序遍历:')
tree.post_order_recursion(tree.root)
print( '\n堆栈实现后序遍历:')
tree.post_order_stack(tree.root)
print ('\n\n队列实现层次遍历:')
tree.level_order_queue(tree.root)