Python uses the zipper method to implement the dictionary method example, python zipper

Python uses the zipper method to implement the dictionary method example, python zipper

Preface

A dictionary is also called a discrete list. The greatest feature is that it uses keys to find its corresponding values. Its time complexity is O (1 ), the following article introduces how to implement the dictionary using the zipper method in python.

In Python, how does one use a list to implement a dictionary?

The biggest problem with dictionary implementation by list is to solve the hash conflict. What should I do if the same location is obtained by calculating different keys in the list?

The simplest way is to use the zipper method.

Zipper: adds another list to each position in a list, so that a hash conflict can be stored. When the selected hash function is good enough,

The number of num is large enough to ensure that each list in the list contains only one element. The location of the element calculated based on the key.

Time to O (1.

Example

Class MyDict: def _ init _ (self, num = 100): # specify the list size self. _ num = num self. _ lst = [] for _ in range (self. _ num): self. _ lst. append ([]) def update (self, key, value): # Add key-value key_index = hash (key) % self. _ num for I, (k, v) in enumerate (self. _ lst [key_index]): if key = k: self. _ lst [key_index] [I] = [key, value] break else: self. _ lst [key_index]. append ([key, value]) def get (self, key): # pop-up value key_index = hash (key) % self based on the specified key. _ num for k, v in self. _ lst [key_index]: if k = key: return v else: raise KeyError ('no such {} key '. format (key) def pop (self, key): # based on the key pop-up element and delete key_index = hash (key) % self. _ num for I, (k, v) in enumerate (self. _ lst [key_index]): if k = key: result = v self. _ lst. pop (I) return result else: raise KeyError ('no such {} key '. format (key) def _ getitem _ (self, key): # You can use a subscript to set key_index = hash (key) % self. _ num for k, v in self. _ lst [key_index]: if k = key: return v else: raise KeyError ('no such {} key '. format (key) def keys (self): # obtain all keys for index in range (self. _ num): for k, v in self. _ lst [index]: yield k def values (self): # obtain all values for index in range (self. _ num): for k, v in self. _ lst [index]: yield v def items (self): # retrieve all entries for index in range (self. _ num): for item in self. _ lst [index]: yield item

Time found by key, visible

Summary

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