import Foundation
let pattern = ##"""
(?<![abc]) # No "a", "b", "c" allowed immediately on the left
(?=(?:[bc]*a){3}) # At least three "a"s
(?=(?:[ac]*b){3}) # At least three "b"s
(?: # Either
(?=[ab]*(?![abc])) # only "a" or "b"s allowed until a location not followed with "a", "b" or "c"
| # or
(?=(?:[ab]*c){3}) # At least three "c"s
)
[abc]+ # Match and consume one or more "a", "b" or "c" chars
"""##
let regex = try! NSRegularExpression(pattern: pattern, options: [.anchorsMatchLines, .allowCommentsAndWhitespace])
let testString = #"""
Examples for valid sequences:
aaabbb
ababab
aaabbbccc
abcabcabc
ababcabcc
Examples for invalid sequences (as a whole):
aaabbbc
aabbb
abbccc
abcabca
"""#
let stringRange = NSRange(location: 0, length: testString.utf16.count)
let matches = regex.matches(in: testString, range: stringRange)
var result: [[String]] = []
for match in matches {
var groups: [String] = []
for rangeIndex in 1 ..< match.numberOfRanges {
let nsRange = match.range(at: rangeIndex)
guard !NSEqualRanges(nsRange, NSMakeRange(NSNotFound, 0)) else { continue }
let string = (testString as NSString).substring(with: nsRange)
groups.append(string)
}
if !groups.isEmpty {
result.append(groups)
}
}
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