Created
November 1, 2017 22:07
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Resolution of a Facebook iOS Code Challenge.
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import Foundation | |
/* | |
A telephone keypad has letters associated with each number (e.g. 2 = abc, 3 = def). | |
Given a passphrase of "fb1" (e.g. one that you might use to log into a bank account), | |
come up with an algorithm that would assemble an array that contains all the different | |
possible letter combinations that, when typed into a telephone dial pad, would be equivalent | |
to the original passphrase. That is, "fb1" equals "321" numerically; matching equivalent | |
combinations include: "da1", "db1", "dc1", "ea1", "eb1", "ec1", "fa1" and "fc1". | |
*/ | |
func getEquivalentStrings(for string: String) -> [String] { | |
let keypadDictionary = [1: ["1"], | |
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"], | |
0: ["0"]] | |
let characterStrings = string.map { "\($0)" } //[String] | |
let relatedLettersArray = characterStrings.map { characterString in Array(keypadDictionary.values).filter { $0.contains { $0 == characterString }}.first! } //[[String]] | |
func allCombinations(for array: [[String]]) -> [String] { | |
guard let firstArray = array.first else { | |
return [""] | |
} | |
return firstArray.flatMap { string in allCombinations(for: Array(array.dropFirst())).map { string + $0 } } | |
} | |
return allCombinations(for: relatedLettersArray).filter { $0 != string } //[String] | |
} | |
let pass = "fb1" | |
let equivalentPassStrings = getEquivalentStrings(for: pass) | |
print(equivalentPassStrings) |
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