46. Permutations

Given a collection of distinct 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],
  [3,2,1]
]

题解

该题是求所有可能的排列组合，是一道典型的dfs类型的题

代码（python实现）

import copy
class Solution(object):
    def permute(self, nums):
        """
        :type nums: List[int]
        :rtype: List[List[int]]
        """
        if nums is None:
            return
        results = []
        if len(nums) == 0:
            return results
        self.helper(nums, results, [])
        return results
    def helper(self, nums, results, list):
        
        if len(list) == len(nums):
            #注意此处是深度拷贝，如果用java语言写则以list为输入new出一个新的实例
            results.append(copy.deepcopy(list))
            return
            
        
        for i in range(len(nums)):
            if(nums[i] in list):
                continue
            
            list.append(nums[i])
            self.helper(nums, results, list)
            list.pop()