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junebash/CommonChars.Swift

Created January 29, 2020 16:59
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Revisions

  1. Jon Bash created this gist Jan 29, 2020.
    76 changes: 76 additions & 0 deletions CommonChars.Swift
    View file
    Original file line number Diff line number Diff line change
    @@ -0,0 +1,76 @@
    func commonChars(_ inputs: [String]) -> [String] {
    guard let lastString = inputs.last else { return [] }

    var commonCountedChars = CountedSet<String>()
    for char in lastString {
    commonCountedChars.add(String(char))
    }
    var strings = inputs
    strings.removeLast()
    // removing last is more computationally efficient than removing first in Swift

    for string in strings {
    var stringCountedChars = CountedSet<String>()
    for char in string {
    stringCountedChars.add(String(char))
    }
    for (commonChar, commonCount) in commonCountedChars.asDictionary {
    if let stringCharCount = stringCountedChars.count(for: commonChar) {
    if stringCharCount < commonCount {
    commonCountedChars.remove(commonChar, count: commonCount - stringCharCount)
    }
    } else {
    commonCountedChars.removeAll(of: commonChar)
    }
    }
    }

    return commonCountedChars.asArray
    }

    struct CountedSet<Element: Hashable> {
    private var dict = [Element: UInt]()

    var asArray: [Element] {
    var array = [Element]()
    for (element, count) in dict {
    array.append(contentsOf: [Element](repeating: element, count: Int(count)))
    }
    return array
    }

    var asDictionary: [Element: UInt] { dict }

    init() {}

    init(from array: [Element]) {
    for element in array {
    if self.dict.keys.contains(element) {
    self.dict[element]! += 1
    } else {
    self.dict[element] = 1
    }
    }
    }

    func count(for element: Element) -> UInt? {
    return (dict[element] != nil) ? dict[element]! : nil
    }

    mutating func add(_ element: Element) {
    dict[element] = (dict[element] == nil) ? 1 : dict[element]! + 1
    }

    mutating func remove(_ element: Element, count removingCount: UInt = 1) {
    if let currentCount = dict[element] {
    dict[element] = (currentCount <= removingCount) ? nil : currentCount - removingCount
    }
    }

    mutating func removeAll(of element: Element) {
    dict[element] = nil
    }
    }

    print(commonChars(["bella","label","roller"]))
    print(commonChars(["cool","lock","cook"]))