#import <Foundation/Foundation.h>

NSArray *changeTo(NSMutableArray*log, NSMutableArray*res){
    if (log.count>0) {
        NSRange loc = {[[log lastObject] integerValue],1};
        NSMutableArray *cop = res.mutableCopy;
        for (NSString *tmp in res) {
            [cop addObject:[tmp stringByReplacingCharactersInRange:loc withString:@"0"]];
            [cop addObject:[tmp stringByReplacingCharactersInRange:loc withString:@"1"]];
            [cop removeObject:tmp];
        }
        [log removeLastObject];
        return changeTo(log, cop);
    }else{
        return res;
    }
}

NSArray *possibilities(NSString *s) {
    NSMutableArray *log = @[].mutableCopy;
    NSMutableArray *res = @[].mutableCopy;
    for (int i = 0; i<s.length; i++) {
        if ([s characterAtIndex:i]=='?') {
            [log addObject:@(i)];
        }
    }
    [res addObject:s];

    NSArray *tol = changeTo(log , res);
    
    return tol;
}

简化版：

#import <Foundation/Foundation.h>

NSArray *possibilities(NSString *s) {
  // NSLog(@"User `possibilities` accidentally invoked!\n");
  if ([s rangeOfString: @"?"].length == 0) return @[s];
  NSString *r = [s stringByReplacingOccurrencesOfString: @"?" withString: @"0" options: 0 range: [s rangeOfString: @"?"]], *t = [s stringByReplacingOccurrencesOfString: @"?" withString: @"1" options: 0 range: [s rangeOfString: @"?"]];
  return [possibilities(r) arrayByAddingObjectsFromArray: possibilities(t)];
}