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39. Combination Sum

문제 링크

https://leetcode.com/problems/combination-sum/description/

문제 설명

Given an array of distinct integers candidates and a target integer target, return a list of all unique combinations of candidates where the chosen numbers sum to target. You may return the combinations in any order.

The same number may be chosen from candidates an unlimited number of times. Two combinations are unique if the frequency of at least one of the chosen numbers is different.

The test cases are generated such that the number of unique combinations that sum up to target is less than 150 combinations for the given input.

제한 사항

  • 1 <= n <= 20
  • 1 <= k <= n

입출력 예 #1

  1. Input : candidates = [2,3,6,7], target = 7
  2. Output : [[2,2,3],[7]]
  3. Explanation : 2 and 3 are candidates, and 2 + 2 + 3 = 7. Note that 2 can be used multiple times.

7 is a candidate, and 7 = 7.

These are the only two combinations.

입출력 예 #2

  1. Input : candidates = [2,3,5], target = 8
  2. Output : [[2,2,2,2],[2,3,3],[3,5]]

입출력 예 #3

  1. Input : candidates = [2], target = 1
  2. Output : []

문제 풀이

dfs 기법을 이용하여 중복 조합 그래프 탐색으로 해결 할 수 있다.

class Solution:
    def combinationSum(self, candidates: List[int], target: int) -> List[List[int]]:
        results = []

        def dfs(csum, index, path) :
            if csum < 0 :
                return
            elif csum == 0 :
                results.append(path)
                return

            for i in range(index, len(candidates)) :
                dfs(csum - candidates[i], i, path + [candidates[i]])

        dfs(target, 0, [])
        return results

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