LeetCode——Permutations

Permutations

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].

用Python递归求全排列，回顾回顾

class Permutations:

    def perm(self, num, li, start, end):

        s = []

        if start == end:

            for i in num:

                s.append(i)

            li.append(s)

        else:

            for i in range(start, end):

                num[start], num[i] = num[i], num[start]

                self.perm(num, li, start + 1, end)

                num[start], num[i] = num[i], num[start]



    # @param num, a list of integer

    # @return a list of lists of integers



    def permute(self, num):

        li = []

        if len(num) == 0:

            return []

        if len(num) == 1:

            return [num]

        self.perm(num, li, 0, len(num))

        return li





pe = Permutations()

pe.permute([3, 2, 1])