Backtracking_Leetcode_17. Letter Combinations of a Phone Number

https://leetcode.com/problems/letter-combinations-of-a-phone-number/submissions/1585290142/?envType=study-plan-v2&envId=top-100-liked

 

문제접근

1. digits을 적절한 알파벳들로 변형

2. 기존 결과값에 해당 알파벳을 추가하여 대체

정답코드

class Solution {
    func letterCombinations(_ digits: String) -> [String] {
        var sol = [String]()

        for digit in digits {
            var subset = [String]()
            let converted = transform(digit)
            if sol.isEmpty {
                subset = converted.map { String($0) }
            } else {
                for char in converted {
                    let base = sol.map {
                        $0 + String(char)
                    }
                    subset.append(contentsOf: base)
                }
            }
            sol = subset
        }
        return sol
    }

    func transform(_ input: Character) -> String {
        switch input {
            case "2": return "abc"
            case "3": return "def"
            case "4": return "ghi"
            case "5": return "jkl"
            case "6": return "mno"
            case "7": return "pqrs"
            case "8": return "tuv"
            case "9": return "wxyz"
            default: return ""
        }
    }
}