Similar question to Recursive pattern in regex, but in Objective-C.

I want to find the ranges or substrings of outer brackets.

Example input:

NSString *input = @"{a {b c}} {d e}";

Example result:

// yeah, I know, we can't put NSRange in an array, it is just to illustrate

NSArray *matchesA = @[NSMakeRange(0, 9), NSMakeRange(10, 5)];  // OK

NSArray *matchesB = @[NSMakeRange(1, 7), NSMakeRange(11, 3)];  // OK too



NSArray *outputA = @[@"{a {b c}}", @"{d e}"];  // OK

NSArray *outputB = @[@"a {b c}", @"d e"];      // OK too

Unfortunately, NSRegularExpression does not accept ?R apparently. Any alternative to match the outer brackets?

Going for manual solution.

Assuming:

NSString *text = @"{a {b c}} {d e}";

nice solution without regex

NSUInteger len = text.length;

unichar buffer[len + 1];

[text getCharacters:buffer range:NSMakeRange(0, len)];

NSMutableOrderedSet<NSValue *> *results = [NSMutableOrderedSet orderedSet];

NSInteger depth = 0;

NSUInteger location = NSNotFound;

for (NSUInteger i = 0; i < len; i++) {

    if (buffer[i] == '{')

    {

        if (depth == 0)

            location = i;

        depth++;

    }

    else if (buffer[i] == '}')

    {

        depth--;

        if (depth == 0)

            [results addObject:[NSValue valueWithRange:NSMakeRange(location, i - location + 1)]];

    }

}



return results;

ugly solution with regex

NSString *innerPattern = @"\{[^{}]*\}";

NSRegularExpression *innerBracketsRegExp = [NSRegularExpression regularExpressionWithPattern:innerPattern options:0 error:nil];

// getting deepest matches

NSArray<NSTextCheckingResult *> *deepestMatches = [innerBracketsRegExp matchesInString:text options:0 range:NSMakeRange(0, text.length)];

// stripping them from text

text = [text stringByReplacingOccurrencesOfString:innerPattern withString:@"" options:NSRegularExpressionSearch range:NSMakeRange(0, text.length)];

// getting new deepest matches

NSArray<NSTextCheckingResult *> *depth2Matches = [innerBracketsRegExp matchesInString:text options:0 range:NSMakeRange(0, text.length)];



// merging the matches of different depth

NSMutableOrderedSet<NSValue *> *results = [NSMutableOrderedSet orderedSet];

for (NSTextCheckingResult *cr in depth2Matches) {

    [results addObject:[NSValue valueWithRange:cr.range]];

}

for (NSTextCheckingResult *cr in deepestMatches) {

    __block BOOL merged = NO;

    [results enumerateObjectsUsingBlock:^(NSValue * _Nonnull value, NSUInteger idx, BOOL * _Nonnull stop) {

        if (merged)

            [results replaceObjectAtIndex:idx withObject:[NSValue valueWithRange:NSMakeRange(value.rangeValue.location + cr.range.length, value.rangeValue.length)]];

        else if (NSLocationInRange(cr.range.location, value.rangeValue))

        {

            [results replaceObjectAtIndex:idx withObject:[NSValue valueWithRange:NSMakeRange(value.rangeValue.location, value.rangeValue.length + cr.range.length)]];

            merged = YES;

        }

        else if (cr.range.location < value.rangeValue.location)

        {

            [results insertObject:[NSValue valueWithRange:cr.range] atIndex:idx];

            merged = YES;

        }

    }];

    if (!merged)

        [results addObject:[NSValue valueWithRange:cr.range]];

}



return results;