NSStringFromIndexSet()

gistfile1.m

NSString * NSStringFromIndexSet(NSIndexSet *indexSet) {
    NSMutableString *string = nil;

    NSRange range = NSMakeRange([indexSet firstIndex], 1);
    while (range.location != NSNotFound) {
        NSUInteger nextIndex = [indexSet indexGreaterThanIndex:range.location];
        while (nextIndex == range.location + range.length) {
            range.length++;
            nextIndex = [indexSet indexGreaterThanIndex:nextIndex];
        }

        if (string == nil) {
            string = [NSMutableString string];
        } else if (string.length) {
            [string appendString:@","];
        }

        if (range.length == 1) {
            [string appendFormat:@"%u", range.location];
        } else {
            NSUInteger firstIndex = range.location;
            NSUInteger lastIndex = firstIndex + range.length - 1;
            [string appendFormat:@"%u-%u", firstIndex, lastIndex];
        }

        range.location = nextIndex;
        range.length = 1;
    }

    return string;
}