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permutations.py
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permutations.py
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# Time: O(n * n!)
# Space: O(n)
#
# Given a collection of numbers, return all possible permutations.
#
# For example,
# [1,2,3] have the following permutations:
# [1,2,3], [1,3,2], [2,1,3], [2,3,1], [3,1,2], and [3,2,1].
#
class Solution:
# @param num, a list of integer
# @return a list of lists of integers
def permute(self, num):
result = []
used = [False] * len(num)
self.permuteRecu(result, used, [], num)
return result
def permuteRecu(self, result, used, cur, num):
if len(cur) == len(num):
result.append(cur + [])
return
for i in xrange(len(num)):
if not used[i]:
used[i] = True
cur.append(num[i])
self.permuteRecu(result, used, cur, num)
cur.pop()
used[i] = False
if __name__ == "__main__":
print Solution().permute([1, 2, 3])