python学习记录（四）-意想不到

计数

from collections import Counter

# 计数

res = Counter(['a','b','a','c','a','b'])

print(res,type(res))

# Counter({'a': 3, 'b': 2, 'c': 1}) <class 'collections.Counter'>

print(dict(res)) # {'a': 3, 'b': 2, 'c': 1}

# 按次数创建容器

res = Counter(a=3,b=2,c=0)

print(list(res.elements())) # ['a', 'a', 'a', 'b', 'b']

# 最常见排序

res = Counter('abcefcaabf').most_common(3)

print(res,type(res)) # [('a', 3), ('b', 2), ('c', 2)] <class 'list'>

数组中排成最小数(cmp_to_key)

# [3,30,34,59] ==> 3033459

def fun_rules(x,y):

    a,b = x + y,y + x

    if a>b:

        return 1

    elif a<b:

        return -1

    else:

        return 0

import functools

varlist = [3,30,34,59]

varlist = [str(i) for i in varlist]

varlist.sort(key=functools.cmp_to_key(fun_rules))

res = ''.join(varlist)

print(res) # 3033459

数组中排成最小数(全排序)

varlist = [3,30,34,59]

from itertools import permutations

res = list(permutations(varlist))

print(res)

varnew = []

for i in res:

    temp = [str(x) for x in i]

    varnew.append(''.join(temp))

print(varnew)

varnew.sort()

print(varnew[0]) # 3033459

全排列

from itertools import permutations

# 不指定长度

varlist = [1,2,3]

res = permutations(varlist)

print(list(res)) # [(1, 2, 3), (1, 3, 2), (2, 1, 3), (2, 3, 1), (3, 1, 2), (3, 2, 1)]

# 指定长度

res = permutations(varlist,r=2)

print(list(res)) # [(1, 2), (1, 3), (2, 1), (2, 3), (3, 1), (3, 2)]

迪卡尔集

from itertools import product

list1 = ['a','b']

list2 = [1,2]

res = product(list1,list2,repeat=1)

print(list(res)) # [('a', 1), ('a', 2), ('b', 1), ('b', 2)]

排列组合排序

# 不重复

from itertools import combinations

varlist = [2,1,3,4]

res = combinations(varlist,r=2)

print(list(res)) # [(2, 1), (2, 3), (2, 4), (1, 3), (1, 4), (3, 4)]

# 可重复

from itertools import combinations_with_replacement

res = combinations_with_replacement(varlist,r=2)

print(list(res)) # [(2, 2), (2, 1), (2, 3), (2, 4), (1, 1), (1, 3), (1, 4), (3, 3), (3, 4), (4, 4)]

截止到当前位置求和/取最大值

from itertools import accumulate

nums = [1, 3, 2, 4]

print(list(accumulate(nums))) # [1, 4, 6, 10]

print(list(accumulate(nums,max))) # [1, 3, 3, 4]

2个容器取对应值

from itertools import compress

nums1 = ['a','b','c','d']

nums2 = [1, 0, 1, 0]

print(list(compress(nums1, nums2))) # ['a', 'c']

巴特西

python学习记录（四）-意想不到

计数

数组中排成最小数(cmp_to_key)

数组中排成最小数(全排序)

全排列

迪卡尔集

排列组合排序

截止到当前位置求和/取最大值

2个容器取对应值

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