[leetcode] 46. Permutations @ python

最新推荐文章于 2024-11-28 09:45:26 发布

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本文深入探讨了基于深度优先搜索和itertools.permutations模块实现的整数全排列算法。通过两个实例，详细展示了如何从给定的整数集合中生成所有可能的排列组合，并分析了各自的时空复杂度。

Given a collection of distinct integers, return all possible permutations.

Example:

Input: [1,2,3]
Output:
[
[1,2,3],
[1,3,2],
[2,1,3],
[2,3,1],
[3,1,2],
[3,2,1]
]

解法1

使用itertools.permutation, 然后将tuple转化为list
Time: O(n)
Space: O(1)

class Solution:
    def permute(self, nums):
        """
        :type nums: List[int]
        :rtype: List[List[int]]
        """
        ans = list(itertools.permutations(nums, len(nums)))
        ans = [list(tup) for tup in ans]
        return ans

解法2

深度优先算法
Time: O(m), m 是排列组合的长度
Space: O(1)

class Solution:
    def permute(self, nums):
        """
        :type nums: List[int]
        :rtype: List[List[int]]
        """
        res = []
        self.dfs(nums, [], res)
        return res
        
    def dfs(self, nums, path, res):
        # when no nums left, add path to res
        if not nums:
            res.append(path)
        for i in range(len(nums)):
            self.dfs(nums[:i] + nums[i+1:], path+[nums[i]], res)