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first commit: added Knuth-Morris-Pratt and Z algorithms implementation
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‎Knuth-Morris-Pratt/KnuthMorrisPratt.playground/Contents.swift

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//: Playground - noun: a place where people can play
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func ZetaAlgorithm(ptnr: String) -> [Int]? {
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let pattern = Array(ptnr.characters)
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let patternLength: Int = pattern.count
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guard patternLength > 0 else {
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return nil
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}
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var zeta: [Int] = [Int](count: patternLength, repeatedValue: 0)
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var left: Int = 0
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var right: Int = 0
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var k_1: Int = 0
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var betaLength: Int = 0
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var textIndex: Int = 0
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var patternIndex: Int = 0
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for k in 1 ..< patternLength {
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if k > right {
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patternIndex = 0
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while k + patternIndex < patternLength &&
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pattern[k + patternIndex] == pattern[patternIndex] {
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patternIndex = patternIndex + 1
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}
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zeta[k] = patternIndex
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if zeta[k] > 0 {
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left = k
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right = k + zeta[k] - 1
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}
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} else {
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k_1 = k - left + 1
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betaLength = right - k + 1
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if zeta[k_1 - 1] < betaLength {
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zeta[k] = zeta[k_1 - 1]
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} else if zeta[k_1 - 1] >= betaLength {
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textIndex = betaLength
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patternIndex = right + 1
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while patternIndex < patternLength && pattern[textIndex] == pattern[patternIndex] {
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textIndex = textIndex + 1
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patternIndex = patternIndex + 1
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}
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zeta[k] = patternIndex - k
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left = k
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right = patternIndex - 1
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}
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}
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}
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return zeta
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}
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extension String {
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func indexesOf(ptnr: String) -> [Int]? {
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let text = Array(self.characters)
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let pattern = Array(ptnr.characters)
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let textLength: Int = text.count
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let patternLength: Int = pattern.count
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guard patternLength > 0 else {
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return nil
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}
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var suffixPrefix: [Int] = [Int](count: patternLength, repeatedValue: 0)
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var textIndex: Int = 0
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var patternIndex: Int = 0
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var indexes: [Int] = [Int]()
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/* Pre-processing stage: computing the table for the shifts (through Z-Algorithm) */
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let zeta = ZetaAlgorithm(ptnr)
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for patternIndex in (1 ..< patternLength).reverse() {
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textIndex = patternIndex + zeta![patternIndex] - 1
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suffixPrefix[textIndex] = zeta![patternIndex]
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}
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/* Search stage: scanning the text for pattern matching */
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textIndex = 0
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patternIndex = 0
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while textIndex + (patternLength - patternIndex - 1) < textLength {
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while patternIndex < patternLength && text[textIndex] == pattern[patternIndex] {
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textIndex = textIndex + 1
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patternIndex = patternIndex + 1
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}
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if patternIndex == patternLength {
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indexes.append(textIndex - patternIndex)
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}
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if patternIndex == 0 {
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textIndex = textIndex + 1
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} else {
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patternIndex = suffixPrefix[patternIndex - 1]
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}
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}
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guard !indexes.isEmpty else {
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return nil
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}
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return indexes
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}
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}
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/* Examples */
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let dna = "ACCCGGTTTTAAAGAACCACCATAAGATATAGACAGATATAGGACAGATATAGAGACAAAACCCCATACCCCAATATTTTTTTGGGGAGAAAAACACCACAGATAGATACACAGACTACACGAGATACGACATACAGCAGCATAACGACAACAGCAGATAGACGATCATAACAGCAATCAGACCGAGCGCAGCAGCTTTTAAGCACCAGCCCCACAAAAAACGACAATFATCATCATATACAGACGACGACACGACATATCACACGACAGCATA"
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dna.indexesOf("CATA") // [20, 64, 130, 140, 166, 234, 255, 270]
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let concert = "🎼🎹🎹🎸🎸🎻🎻🎷🎺🎤👏👏👏"
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concert.indexesOf("🎻🎷") // [6]

‎Knuth-Morris-Pratt/KnuthMorrisPratt.playground/contents.xcplayground

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<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
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<playground version='5.0' target-platform='osx'>
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<timeline fileName='timeline.xctimeline'/>
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</playground>

‎Knuth-Morris-Pratt/KnuthMorrisPratt.playground/playground.xcworkspace/contents.xcworkspacedata

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Some generated files are not rendered by default. Learn more about customizing how changed files appear on GitHub.

‎Knuth-Morris-Pratt/KnuthMorrisPratt.playground/timeline.xctimeline

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<?xml version="1.0" encoding="UTF-8"?>
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<Timeline
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version = "3.0">
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<TimelineItems>
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</TimelineItems>
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</Timeline>

‎Knuth-Morris-Pratt/KnuthMorrisPratt.swift

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/* Knuth-Morris-Pratt algorithm for pattern/string matching
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The code is based on the book:
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"Algorithms on String, Trees and Sequences: Computer Science and Computational Biology"
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by Dan Gusfield
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Cambridge University Press, 1997
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*/
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import Foundation
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extension String {
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func indexesOf(ptnr: String) -> [Int]? {
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let text = Array(self.characters)
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let pattern = Array(ptnr.characters)
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let textLength: Int = text.count
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let patternLength: Int = pattern.count
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guard patternLength > 0 else {
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return nil
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}
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var suffixPrefix: [Int] = [Int](count: patternLength, repeatedValue: 0)
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var textIndex: Int = 0
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var patternIndex: Int = 0
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var indexes: [Int] = [Int]()
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/* Pre-processing stage: computing the table for the shifts (through Z-Algorithm) */
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let zeta = ZetaAlgorithm(ptnr)
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for patternIndex in (1 ..< patternLength).reverse() {
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textIndex = patternIndex + zeta![patternIndex] - 1
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suffixPrefix[textIndex] = zeta![patternIndex]
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}
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/* Search stage: scanning the text for pattern matching */
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textIndex = 0
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patternIndex = 0
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while textIndex + (patternLength - patternIndex - 1) < textLength {
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while patternIndex < patternLength && text[textIndex] == pattern[patternIndex] {
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textIndex = textIndex + 1
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patternIndex = patternIndex + 1
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}
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if patternIndex == patternLength {
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indexes.append(textIndex - patternIndex)
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}
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if patternIndex == 0 {
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textIndex = textIndex + 1
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} else {
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patternIndex = suffixPrefix[patternIndex - 1]
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}
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}
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guard !indexes.isEmpty else {
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return nil
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}
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return indexes
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}
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}

‎Z-Algorithm/ZAlgorithm.swift

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/* Z-Algorithm for pattern/string pre-processing
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The code is based on the book:
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"Algorithms on String, Trees and Sequences: Computer Science and Computational Biology"
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by Dan Gusfield
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Cambridge University Press, 1997
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*/
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import Foundation
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func ZetaAlgorithm(ptrn: String) -> [Int]? {
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let pattern = Array(ptrn.characters)
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let patternLength: Int = pattern.count
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guard patternLength > 0 else {
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return nil
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}
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var zeta: [Int] = [Int](count: patternLength, repeatedValue: 0)
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var left: Int = 0
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var right: Int = 0
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var k_1: Int = 0
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var betaLength: Int = 0
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var textIndex: Int = 0
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var patternIndex: Int = 0
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for k in 1 ..< patternLength {
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if k > right {
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patternIndex = 0
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while k + patternIndex < patternLength &&
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pattern[k + patternIndex] == pattern[patternIndex] {
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patternIndex = patternIndex + 1
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}
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zeta[k] = patternIndex
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if zeta[k] > 0 {
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left = k
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right = k + zeta[k] - 1
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}
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} else {
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k_1 = k - left + 1
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betaLength = right - k + 1
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if zeta[k_1 - 1] < betaLength {
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zeta[k] = zeta[k_1 - 1]
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} else if zeta[k_1 - 1] >= betaLength {
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textIndex = betaLength
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patternIndex = right + 1
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while patternIndex < patternLength && pattern[textIndex] == pattern[patternIndex] {
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textIndex = textIndex + 1
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patternIndex = patternIndex + 1
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}
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zeta[k] = patternIndex - k
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left = k
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right = patternIndex - 1
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}
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}
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}
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return zeta
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}

‎Z-Algorithm/ZetaAlgorithm.playground/Contents.swift

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//: Playground - noun: a place where people can play
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func ZetaAlgorithm(ptrn: String) -> [Int]? {
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let pattern = Array(ptrn.characters)
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let patternLength: Int = pattern.count
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guard patternLength > 0 else {
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return nil
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}
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var zeta: [Int] = [Int](count: patternLength, repeatedValue: 0)
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var left: Int = 0
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var right: Int = 0
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var k_1: Int = 0
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var betaLength: Int = 0
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var textIndex: Int = 0
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var patternIndex: Int = 0
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for k in 1 ..< patternLength {
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if k > right {
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patternIndex = 0
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while k + patternIndex < patternLength &&
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pattern[k + patternIndex] == pattern[patternIndex] {
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patternIndex = patternIndex + 1
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}
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zeta[k] = patternIndex
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if zeta[k] > 0 {
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left = k
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right = k + zeta[k] - 1
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}
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} else {
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k_1 = k - left + 1
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betaLength = right - k + 1
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if zeta[k_1 - 1] < betaLength {
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zeta[k] = zeta[k_1 - 1]
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} else if zeta[k_1 - 1] >= betaLength {
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textIndex = betaLength
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patternIndex = right + 1
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while patternIndex < patternLength && pattern[textIndex] == pattern[patternIndex] {
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textIndex = textIndex + 1
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patternIndex = patternIndex + 1
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}
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zeta[k] = patternIndex - k
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left = k
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right = patternIndex - 1
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}
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}
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}
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return zeta
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}
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extension String {
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func indexesOf(pattern: String) -> [Int]? {
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let patternLength: Int = pattern.characters.count
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let zeta = ZetaAlgorithm(pattern + "💲" + self)
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guard zeta != nil else {
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return nil
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}
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var indexes: [Int] = [Int]()
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/* Scan the zeta array to find matched patterns */
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for i in 0 ..< zeta!.count {
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if zeta![i] == patternLength {
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indexes.append(i - patternLength - 1)
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}
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}
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guard !indexes.isEmpty else {
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return nil
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}
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return indexes
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}
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}
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/* Examples */
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let str = "Hello, playground!"
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str.indexesOf("ground") // [11]
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let traffic = "🚗🚙🚌🚕🚑🚐🚗🚒🚚🚎🚛🚐🏎🚜🚗🏍🚒🚲🚕🚓🚌🚑"
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traffic.indexesOf("🚑") // [4, 21]

‎Z-Algorithm/ZetaAlgorithm.playground/contents.xcplayground

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<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
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<playground version='5.0' target-platform='osx'>
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<timeline fileName='timeline.xctimeline'/>
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</playground>

‎Z-Algorithm/ZetaAlgorithm.playground/playground.xcworkspace/contents.xcworkspacedata

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Some generated files are not rendered by default. Learn more about customizing how changed files appear on GitHub.

‎Z-Algorithm/ZetaAlgorithm.playground/timeline.xctimeline

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<?xml version="1.0" encoding="UTF-8"?>
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<Timeline
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version = "3.0">
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<TimelineItems>
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</TimelineItems>
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</Timeline>

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