[Leetcode/파이썬] 77. Combinations

Combinations

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Given two integers n and k, return all possible combinations of k numbers chosen from the range [1, n].

You may return the answer in any order.

 

Example 1:

Input: n = 4, k = 2
Output: [[1,2],[1,3],[1,4],[2,3],[2,4],[3,4]]
Explanation: There are 4 choose 2 = 6 total combinations.
Note that combinations are unordered, i.e., [1,2] and [2,1] are considered to be the same combination.

Example 2:

Input: n = 1, k = 1
Output: [[1]]
Explanation: There is 1 choose 1 = 1 total combination.

 

Constraints:

• 1 <= n <= 20
• 1 <= k <= n

 

class Solution:
    def combine(self, n: int, k: int) -> List[List[int]]:
        res = []
        output = []
        def dfs(start) :
            if len(output) == k :
                res.append(output[:])
                return
            
            for idx in range(start, n+1):
                output.append(idx)
                dfs(idx + 1)
                output.pop()

        dfs(1)
        return res

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