import Foundation
let pattern = #"(?<= |^)(\S+)(?: \1){2,}(?= |$)"#
let regex = try! NSRegularExpression(pattern: pattern, options: .anchorsMatchLines)
let testString = #"""
hi hi hi hi some words words words which'll repeat repeat repeat repeat repeat
t.he he hemisphere
bye! bye! bye!
he he he he hemisphere
"""#
let stringRange = NSRange(location: 0, length: testString.utf16.count)
let substitutionString = #"\1 \1"#
let result = regex.stringByReplacingMatches(in: testString, range: stringRange, withTemplate: substitutionString)
print(result)
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for Swift 5.2, please visit: https://developer.apple.com/documentation/foundation/nsregularexpression