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PaulWoodIII/ReverseWordsInAString.swift

Created August 31, 2019 00:14
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  1. PaulWoodIII created this gist Aug 31, 2019.
    72 changes: 72 additions & 0 deletions ReverseWordsInAString.swift
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    Original file line number Diff line number Diff line change
    @@ -0,0 +1,72 @@
    //
    // main.swift
    // ReverseWordsInAString
    //
    // Created by Paul Wood on 8/30/19.
    // Copyright © 2019 Paul Wood. All rights reserved.
    //

    import Foundation

    let sentence = "Words to reverse in a String"
    let emptySentence = ""
    let single = "a"

    // Not very performant but very readable
    func reverseWords(_ input: String) -> String {
    return input
    .components(separatedBy: .whitespacesAndNewlines)
    .map { (string) -> String in
    return String(string.reversed())
    }.joined(separator: " ")
    }

    // Reverse the words In place and in O(N) String is not subscriptable so we work around it with a [Character]
    func reverseSentence(_ input: inout [Character]) {
    var wordStart = 0
    var wordEnd = 0
    var whitespace = 0

    func reverse(_ input: inout [Character], start: inout Int, end: inout Int) {
    while start < end {
    let temp = input[start]
    input[start] = input[end]
    input[end] = temp
    start += 1
    end -= 1
    }
    }

    while whitespace < input.count {
    if input[whitespace].isWhitespace {
    reverse(&input, start: &wordStart, end: &wordEnd)
    wordStart = whitespace + 1
    }
    whitespace += 1
    wordEnd = whitespace - 1
    }
    if whitespace != 0 {
    reverse(&input, start: &wordStart, end: &wordEnd)
    }
    }

    print(sentence)
    print(reverseWords(sentence))
    print(reverseWords(emptySentence))
    print(reverseWords(single))

    var sentenceArray = sentence.map { (c) -> Character in
    return c
    }
    reverseSentence(&sentenceArray)
    print( String(sentenceArray))

    var singleArray = single.map { (c) -> Character in
    return c
    }
    reverseSentence(&singleArray)
    print( String(singleArray))

    var emptyArray: [Character] = []
    reverseSentence(&emptyArray)
    print( String(emptyArray))