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学习编程、学习Python最好的方式就是练习,哪怕是新手,只要不断地敲代码输出,肯定会有神效。
Python的练手项目很多,特别是Github上,建议不管新手、老司机都去看看。
这里推荐给大家一个Gitthub上练习的项目,算法仓库-algorithms。
https://github.com/keon/algorithms
这里面集合众多核心算法的Python实现,比如排序、图计算、回溯、队列、流计算、堆、搜索、压缩等等。
该仓库支持第三方库安装,在python中进行调用,非常方便。
首先使用pip进行安装:
pip3 install algorithms
然后导入相关模块进行调用,比如sort模块里的merge_sort归并排序算法。
- from algorithms.sort import merge_sort
-
- if __name__ == "__main__":
- my_list = [1, 8, 3, 5, 6]
- my_list = merge_sort(my_list)
- print(my_list)
举几个常见的算法案例。
- def bucket_sort(arr):
- ''' Bucket Sort
- Complexity: O(n^2)
- The complexity is dominated by nextSort
- '''
- # The number of buckets and make buckets
- num_buckets = len(arr)
- buckets = [[] for bucket in range(num_buckets)]
- # Assign values into bucket_sort
- for value in arr:
- index = value * num_buckets // (max(arr) + 1)
- buckets[index].append(value)
- # Sort
- sorted_list = []
- for i in range(num_buckets):
- sorted_list.extend(next_sort(buckets[i]))
- return sorted_list
-
- def next_sort(arr):
- # We will use insertion sort here.
- for i in range(1, len(arr)):
- j = i - 1
- key = arr[i]
- while arr[j] > key and j >= 0:
- arr[j+1] = arr[j]
- j = j - 1
- arr[j + 1] = key
- return arr

- import math
-
- def distance(x,y):
- """[summary]
- HELPER-FUNCTION
- calculates the (eulidean) distance between vector x and y.
- Arguments:
- x {[tuple]} -- [vector]
- y {[tuple]} -- [vector]
- """
- assert len(x) == len(y), "The vector must have same length"
- result = ()
- sum = 0
- for i in range(len(x)):
- result += (x[i] -y[i],)
- for component in result:
- sum += component**2
- return math.sqrt(sum)
-
- def nearest_neighbor(x, tSet):
- """[summary]
- Implements the nearest neighbor algorithm
- Arguments:
- x {[tupel]} -- [vector]
- tSet {[dict]} -- [training set]
- Returns:
- [type] -- [result of the AND-function]
- """
- assert isinstance(x, tuple) and isinstance(tSet, dict)
- current_key = ()
- min_d = float('inf')
- for key in tSet:
- d = distance(x, key)
- if d < min_d:
- min_d = d
- current_key = key
- return tSet[current_key]

- # Implement the encode and decode methods.
-
- def encode(strs):
- """Encodes a list of strings to a single string.
- :type strs: List[str]
- :rtype: str
- """
- res = ''
- for string in strs.split():
- res += str(len(string)) + ":" + string
- return res
-
- def decode(s):
- """Decodes a single string to a list of strings.
- :type s: str
- :rtype: List[str]
- """
- strs = []
- i = 0
- while i < len(s):
- index = s.find(":", i)
- size = int(s[i:index])
- strs.append(s[index+1: index+1+size])
- i = index+1+size
- return strs

- def get_histogram(input_list: list) -> dict:
- """
- Get histogram representation
- :param input_list: list with different and unordered values
- :return histogram: dict with histogram of input_list
- """
- # Create dict to store histogram
- histogram = {}
- # For each list value, add one to the respective histogram dict position
- for i in input_list:
- histogram[i] = histogram.get(i, 0) + 1
- return histogram
个人感觉这个仓库里的算法很齐全,适合做练习,小伙伴们可以试试。
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