LeetCode-Solutions/Python/permutations.py at master · pythonpeixun/LeetCode-Solutions · GitHub

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# Time: O(n * n!)

# Space: O(n)

class Solution(object):

# @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

# Time: O(n^2 * n!)

# Space: O(n^2)

class Solution2(object):

def permute(self, nums):

"""

:type nums: List[int]

:rtype: List[List[int]]

"""

res = []

self.dfs(nums, [], res)

return res

def dfs(self, nums, path, res):

if not nums:

res.append(path)

for i in xrange(len(nums)):

# e.g., [1, 2, 3]: 3! = 6 cases

# idx -> nums, path

# 0 -> [2, 3], [1] -> 0: [3], [1, 2] -> [], [1, 2, 3]

# -> 1: [2], [1, 3] -> [], [1, 3, 2]

# 1 -> [1, 3], [2] -> 0: [3], [2, 1] -> [], [2, 1, 3]

# -> 1: [1], [2, 3] -> [], [2, 3, 1]

# 2 -> [1, 2], [3] -> 0: [2], [3, 1] -> [], [3, 1, 2]

# -> 1: [1], [3, 2] -> [], [3, 2, 1]

self.dfs(nums[:i] + nums[i+1:], path + [nums[i]], res)

LeetCode-Solutions/Python/permutations.py at master · pythonpeixun/LeetCode-Solutions · GitHub

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