# Share my Python solution (Narayana Pandita's algorithm)

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``````class Solution:
# @param {integer[]} nums
# @return {void} Do not return anything, modify nums in-place instead.
def nextPermutation(self, nums):
'''
Narayana Pandita's algorithm
1. Find the largest index k such that a[k] < a[k + 1]. If no such index exists, the permutation is the last permutation.
2. Find the largest index l greater than k such that a[k] < a[l].
3. Swap the value of a[k] with that of a[l].
4. Reverse the sequence from a[k + 1] up to and including the final element a[n].
'''
# scan backward to find the first element that is bigger than the element before it
i = len(nums) - 1
while i > 0 and nums[i] <= nums[i-1]:
i -= 1
if i > 0:
# find the smallest number after nums[i] that is bigger than nums[i-1]
j = len(nums) - 1
while nums[j] <= nums[i-1]:
j -= 1
# swap nums[j] with nums[i-1]
nums[i-1], nums[j] = nums[j], nums[i-1]
# reverse the part after i
nums[i:] = reversed(nums[i:])``````

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