Next Permutation — LeetCode 31 Python Solution

The problem

A permutation of an array of integers is an arrangement of its members into a sequence or linear order. For example, for arr = [1,2,3], the following are all the permutations of arr: [1,2,3], [1,3,2], [2, 1, 3], [2, 3, 1], [3,1,2], [3,2,1].

Example

Input

nums = [1,2,3]

Output

[1,3,2]

Python solution

class Solution:
    def nextPermutation(self, nums: List[int]) -> None:
        n = len(nums)
        i = next((i for i in range(n - 2, -1, -1) if nums[i] < nums[i + 1]), -1)
        if ~i:
            j = next((j for j in range(n - 1, i, -1) if nums[j] > nums[i]))
            nums[i], nums[j] = nums[j], nums[i]
        nums[i + 1 :] = nums[i + 1 :][::-1]

Complexity

Pattern: Two Pointers

Use the order already in the input to discard half the search space at every step. LeetCode 31. Next Permutation is filed here on both counts: the reference solution below belongs to the algorithm family this hub collects, and LeetCode tags it Two Pointers.

The two pointers guide has the Python template for the pattern and the 201 LeetCode problems that use it.

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