39. Combination Sum

2019-04-17

39. Combination Sum

Given a set of candidate numbers (candidates) (without duplicates) and a target number (target), find all unique combinations in candidates where the candidate numbers sums to target.

The same repeated number may be chosen from candidates unlimited number of times.

Note:

  • All numbers (including target) will be positive integers.
  • The solution set must not contain duplicate combinations.

Example 1:

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Input: candidates = [2,3,6,7], target = 7,
A solution set is:
[
  [7],
  [2,2,3]
]

Example 2:

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Input: candidates = [2,3,5], target = 8,
A solution set is:
[
  [2,2,2,2],
  [2,3,3],
  [3,5]
]

Code:

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class Solution(object):
    def combinationSum(self, candidates, target):
        res = []
        candidates.sort()
        self.dfs(candidates, target, 0, [], res)
        return res

    def dfs(self, nums, target, index, path, res):
        if target < 0:
            return  # backtracking
        if target == 0:
            res.append(path)
            return
        for i in range(index, len(nums)):
            self.dfs(nums, target-nums[i], i, path+[nums[i]], res)
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