[leetcode]Permutations @ Python

原題地址：https://oj.leetcode.com/problems/permutations/

題意：

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].

解題思路：窮舉一個集合的全排列。這個就是python遞歸巧妙的使用了。

代碼：

class Solution:
    # @param num, a list of integer
    # @return a list of lists of integers
    def permute(self, num):
        if len(num) == 0: return []
        if len(num) == 1: return [num]
        res = []
        for i in range(len(num)):
            for j in self.permute(num[:i] + num[i+1:]):
                res.append([num[i]] + j)
        return res