Combination Sum

## Description

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:

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

Example 2:

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

## Solution

func combinationSum(candidates []int, target int) [][]int {
sort.Ints(candidates)

return doCombinationSum(candidates, target)
}

func doCombinationSum(candidates []int, target int) [][]int {
res := [][]int{}

if len(candidates) == 0 {
return res
}

t := target - candidates[0]

if t < 0 {
return res
} else if t == 0 {
res = append(res, []int{candidates[0]})
} else if t > 0 {
res = doCombinationSum(candidates, t)
for i, v := range res {
res[i] = append([]int{candidates[0]}, v...)
}
}

res = append(res, doCombinationSum(candidates[1:], target)...)

return res
}