letterCombinations

letterCombinations.swift

class Solution {
        var hashMap: [String: String] = ["2": "abc", "3": "def", "4": "ghi", "5": "jkl", "6": "mno", "7": "pqrs", "8": "tuv", "9": "wxyz"]
    func generateCombination(result: String, nextDigit: String, output: inout [String]) {
        if nextDigit.isEmpty {
            output.append(result)
            return
        }else {
            var newDigit = nextDigit
            let firstString = newDigit.removeFirst()
            if let value = hashMap[String(firstString)] {
                let letters = Array(value)
                for letter in letters {
                    generateCombination(result: result + String(letter), nextDigit: newDigit, output: &output)
                }
            }
        }
    }
    func letterCombinations(_ digits: String) -> [String] {
        var output: [String] = []
        if digits.isEmpty == false {
            generateCombination(result: "", nextDigit: digits, output: &output)
        }
        return output
    }
}