Generate all permutation of a set in Python
Permutation is an arrangement of objects in a specific order. Order of arrangement of object is very important. The number of permutations on a set of n elements is given by n!. For example, there are 2! = 2*1 = 2 permutations of {1, 2}, namely {1, 2} and {2, 1}, and 3! = 3*2*1 = 6 permutations of {1, 2, 3}, namely {1, 2, 3}, {1, 3, 2}, {2, 1, 3}, {2, 3, 1}, {3, 1, 2} and {3, 2, 1}.
Method 1 (Backtracking)
We can use the backtracking based recursive solution discussed here.
Method 2
The idea is to one by one extract all elements, place them at first position and recur for remaining list.
Python3
def permutation(lst):
if len (lst) = = 0 :
return []
if len (lst) = = 1 :
return [lst]
l = []
for i in range ( len (lst)):
m = lst[i]
remLst = lst[:i] + lst[i + 1 :]
for p in permutation(remLst):
l.append([m] + p)
return l
data = list ( '123' )
for p in permutation(data):
print (p)
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Output:
['1', '2', '3']
['1', '3', '2']
['2', '1', '3']
['2', '3', '1']
['3', '1', '2']
['3', '2', '1']
Method 3 (Direct Function)
We can do it by simply using the built-in permutation function in itertools library. It is the shortest technique to find the permutation.
Python3
from itertools import permutations
l = list (permutations( range ( 1 , 4 )))
print (l)
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Output:
[(1, 2, 3), (1, 3, 2), (2, 1, 3), (2, 3, 1), (3, 1, 2), (3, 2, 1)]
Last Updated :
21 Jan, 2022
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