[Leetcode]@python 77. Combinations

题目链接

https://leetcode.com/problems/combinations/

题目原文

Given two integers n and k, return all possible combinations of k numbers out of 1 ... n.

For example,
If n = 4 and k = 2, a solution is:

[
[2,4],
[3,4],
[2,3],
[1,2],
[1,3],
[1,4],
]

题目大意

给出C(n,K)的组合

解题思路

使用dfs求解

代码

class Solution(object):
    def combine(self, n, k):
        """
        :type n: int
        :type k: int
        :rtype: List[List[int]]
        """

        ans = []
        self.count = 0

        def dfs(start, valuelist):
            if self.count == k:
                ans.append(valuelist)
                return
            for i in range(start, n + 1):
                self.count += 1
                dfs(i + 1, valuelist + [i])
                self.count -= 1

        dfs(1, [])
        return ans