数据结构复习

Mon, 27 Dec 2021 00:41:50 +0800

1.什么是算法？

算法是计算机科学中的基本概念，是对特定问题的求解步骤

2.什么是算法的复杂度？

分为时间复杂度和空间复杂度，前者一般是指程序运行从开始到结束所需的时间，后者一般是指对应的程序从运行开始到结束所需的储存空间

哈夫曼编码的实现(python)

Sun, 21 Nov 2021 21:31:23 +0800

思路

~~C++实在是弄不懂~~

代码

from typing import List, Optional
class Node:
"""
结点
"""
def __init__(self):
self.name: Optional[str] = None
self.weight: Optional[int] = None
self.left_child: Optional[Node] = None
self.right_child: Optional[Node] = None
self.parent: Optional[Node] = None
class NodeCode:
"""
结点的编码
"""
def __init__(self, name: str, code: str):
self.name = name
self.code = code
def __str__(self):
return f"{self.name}:{self.code}"
class HaffumanTreeCode:
"""
哈夫曼树的编码
"""
def __init__(self):
self.code_list: List[NodeCode] = []
def append(self, code: NodeCode):
self.code_list.append(code)
def code(self, massage: str):
"""
针对编码表编码
:param massage: 需要编码的信息
:return:
"""
code = ""
for i in massage:
for n in self.code_list:
if n.name == i:
code += n.code
break
# raise ValueError(f"'{i}'不存在")
return code
def decode(self, code: str):
"""
针对编码表解码
:param code:需要解码的哈夫曼码
:return:
"""
out = ""
i = 0
while code:
code_need_match = code[0:i+1]
for n in self.code_list:
if n.code == code_need_match:
out += n.name
code = code[i+1:]
i = 0
break
i += 1
return out
def __str__(self):
"""
打印
:return:
"""
out = ""
for i in self.code_list:
out += i.__str__() + "\n"
return out.strip()
class HaffumanTree:
"""
哈夫曼树
"""
def __init__(self):
self.root = Node()
self.nodes: List[Node] = []
self.nodes_raw: List[Node] = []
self.codes: HaffumanTreeCode = HaffumanTreeCode()
def inser(self, newnode: Node):
for i in range(len(self.nodes)):
if self.nodes[i].weight < newnode.weight:
self.nodes.insert(i, newnode)
return
self.nodes.append(newnode)
def build_tree(self, name_list: List[str], weight_list: List[int]):
"""
创建哈夫曼树
:param name_list: 字符列表
:param weight_list: 权重列表
:return:
"""
# 队每个字符生成结点
while len(name_list) > 0:
max_weight = max(weight_list)
max_index = weight_list.index(max_weight)
max_name = name_list[max_index]
newnode = Node()
newnode.name = max_name
newnode.weight = max_weight
self.nodes.append(newnode)
name_list.remove(max_name)
weight_list.remove(max_weight)
# 保存源结点
self.nodes_raw = self.nodes[:]
# 创建新结点并生成树
while len(self.nodes) > 2:
left = self.nodes.pop()
right = self.nodes.pop()
newnode = Node()
newnode.weight = left.weight + right.weight
newnode.left_child = left
newnode.right_child = right
left.parent = newnode
right.parent = newnode
# 根据权重插入
self.inser(newnode)
left = self.nodes.pop()
right = self.nodes.pop()
self.root.weight = left.weight + right.weight
self.root.left_child = left
self.root.right_child = right
left.parent = self.root
right.parent = self.root
def make_code(self):
"""
生成编码表
:return:
"""
while len(self.nodes_raw):
node = self.nodes_raw.pop()
name = node.name
code = ""
while node.parent != self.root:
parent = node.parent
if parent.left_child == node:
code = "0" + code
elif parent.right_child == node:
code = "1" + code
node = parent
if self.root.left_child == node:
code = "0" + code
elif self.root.right_child == node:
code = "1" + code
self.codes.append(NodeCode(name, code))
def decode(self, code: str):
return self.codes.decode(code)
def code(self, massage: str):
return self.codes.code(massage)
if __name__ == '__main__':
h = HaffumanTree()
name_list = ["a", "b", "c", "d", "e"]
wight_list = [5, 11, 6, 21, 19]
h.build_tree(name_list, wight_list)
h.make_code()
print(f"编码表：\n{h.codes}")
print(f'bcacce编码为：{h.code("bcacce")}')
print(f'01001000001001解码为： {h.decode("0100100000100110")}')

数据结构 on kutake小站

数据结构复习

1.什么是算法？

2.什么是算法的复杂度？

哈夫曼编码的实现(python)

思路

代码