39. Combination Sum

39. Combination Sum.swift

class Solution {
    
    func combinationSum(_ candidates: [Int], _ target: Int) -> [[Int]] {
    
        var res = [[Int]]()
        var temp = [Int]()
        helper(&res, &temp, candidates, 0, target)
        return res
    }
    
    func helper(_ res: inout [[Int]], _ temp: inout [Int], _ candidates: [Int], _ index: Int, _ target: Int) {
        //print("res: \(res), temp: \(temp), candidates: \(candidates), index: \(index), target: \(target)")
        if target < 0 { return }
        
        if target == 0 {
            res.append(temp)
            //print("temp is appended")
            return
        }
        
        for i in index ..< candidates.count {
            if candidates[i] == 0 { continue }
            
            temp.append(candidates[i])
            helper(&res, &temp, candidates, i, target - candidates[i]) // 이해안감 왜 target - candidates[i] 인지?
            temp.removeLast()
        }
    }
}

let sol = Solution()
let arr = [2,3,6,7]
print(sol.combinationSum(arr, 7))