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next-permutation.py
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42 lines (37 loc) · 1.21 KB
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# Time: O(n)
# Space: O(1)
#
# Implement next permutation, which rearranges numbers into the lexicographically next greater permutation of numbers.
#
# If such arrangement is not possible, it must rearrange it as the lowest possible order (ie, sorted in ascending order).
#
# The replacement must be in-place, do not allocate extra memory.
#
# Here are some examples. Inputs are in the left-hand column and its corresponding outputs are in the right-hand column.
# 1,2,3 -> 1,3,2
# 3,2,1 -> 1,2,3
# 1,1,5 -> 1,5,1
#
class Solution:
# @param num, a list of integer
# @return a list of integer
def nextPermutation(self, num):
k, l = -1, 0
for i in xrange(len(num) - 1):
if num[i] < num[i + 1]:
k = i
if k == -1:
return num[::-1]
for i in xrange(len(num)):
if num[i] > num[k]:
l = i
num[k], num[l] = num[l], num[k]
return num[:k + 1] + num[:k:-1]
if __name__ == "__main__":
num = [1, 4, 3, 2]
num = Solution().nextPermutation(num)
print num
num = Solution().nextPermutation(num)
print num
num = Solution().nextPermutation(num)
print num