itertools - 조합, 순열

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itertools - 조합, 순열

조합(combinations)	순열(permutations)
순서x	순서o
\(_nC_r\)	\(_nP_r\)
\(\frac{n!}{(n-r)!r!}\)	\(\frac{n!}{(n-r)!}\)

조합

n개 중에서 r개를 뽑는 경우의 수

In [1]:

from itertools import combinations

In [2]:

fruits = ['apple', 'orange', 'banana']

In [3]:

for coms in combinations(fruits, 2):
    print(coms)

Out [3]:

('apple', 'orange')
('apple', 'banana')
('orange', 'banana')

In [4]:

# combinations 구현
for i in range(len(fruits)):
    for j in range(i+1, len(fruits)):
        print((fruits[i], fruits[j]))

Out [4]:

('apple', 'orange')
('apple', 'banana')
('orange', 'banana')

순열

n개 중에서 순서를 정해 r개를 뽑는 경우의 수

In [5]:

from itertools import permutations

In [6]:

fruits = ['apple', 'orange', 'banana']

In [7]:

for perms in permutations(fruits, 2):
    print(perms)

Out [7]:

('apple', 'orange')
('apple', 'banana')
('orange', 'apple')
('orange', 'banana')
('banana', 'apple')
('banana', 'orange')

In [8]:

# permutations 구현
for i in range(len(fruits)):
    for j in range(len(fruits)):
        if i != j:
            print((fruits[i], fruits[j]))

Out [8]:

('apple', 'orange')
('apple', 'banana')
('orange', 'apple')
('orange', 'banana')
('banana', 'apple')
('banana', 'orange')