題目連結：https://leetcode.com/problems/letter-combinations-of-a-phone-number/
法ㄧ: (自己寫的解法)
func letterCombinations(_ digits: String) -> [String] {
let dic: [Character: String] = ["2" : "abc",
"3" : "def",
"4" : "ghi",
"5" : "jkl",
"6" : "mno",
"7" : "pqrs",
"8" : "tuv",
"9" : "wxyz"]
let digitsArr = Array(digits)
var arr: [String] = []
for i in 0 ..< digitsArr.count {
arr.append(dic[digitsArr[i]]!)
}
var result: [String] = []
for i in 0 ..< arr.count {
let tmp = Array(arr[i])
var tmpResult: [String] = []
for j in 0 ..< tmp.count {
if result.count == 0 {
let val = String(tmp[j])
tmpResult.append(val)
} else {
for k in 0 ..< result.count {
let val = String(result[k]) + String(tmp[j])
tmpResult.append(val)
}
}
}
result = tmpResult
}
return result
}法二: (別人寫的解法[Ref])
private let matrix: [Character:[Character]] = ["2":["a","b","c"],
"3":["d","e","f"],
"4":["g","h","i"],
"5":["j","k","l"],
"6":["m","n","o"],
"7":["p","q","r","s"],
"8":["t","u","v"],
"9":["w","x","y","z"]]
func letterCombinations(_ digits: String) -> [String] {
var result: [String] = []
for ch in digits.map({ Character($0.lowercased()) }) {
guard let chars = matrix[ch] else { break }
guard !(result.isEmpty) else {
chars.forEach { result.append("\($0)") }
continue
}
let current = result
result.removeAll()
for ch in chars {
result.append(contentsOf: current.map { $0 + "\(ch)" })
}
}
return result
}