spa-paper/algorithm.m

#import <Foundation/Foundation.h>

@interface Algorithm : NSObject

  @property (atomic, strong) NSMutableArray *permutations;

  - (NSMutableArray *)findPermutations;
  - (void)shift:(long) number shifts: (char) shifts initialSubtraction: (long) initialSubtraction currentShiftIteration:(int)currentShiftIteration currentSubtractionIteration:(int)currentSubtractionIteration;
  - (void)subtract:(long)number subtractions:(char)subtractions initialSubtraction:(long)initialSubtraction currentShiftIteration:(int)currentShiftIteration currentSubtractionIteration:(int)currentSubtractionIteration;

@end

@implementation Algorithm

  @synthesize permutations;

  - (NSMutableArray *)findPermutations
  {
    permutations = [[NSMutableArray alloc] init];
    [permutations addObject:[[NSNumber alloc] initWithChar:31]];
    [self shift:(long)31 shifts:(char)4 initialSubtraction:(long)0 currentShiftIteration:0 currentSubtractionIteration:0];  
    return permutations;
  }

  - (void)shift:(long)number shifts:(char)shifts initialSubtraction:(long)initialSubtraction currentShiftIteration:(int)currentShiftIteration currentSubtractionIteration:(int)currentSubtractionIteration
  {
    if (currentShiftIteration >= 4) {
      return;
    }
    
    for(char b = 0; b < shifts; b++)  {
      if (currentShiftIteration >= 4) {
        return;
      }
      number = (long)((long)number << 1);
      currentShiftIteration++;
      [permutations addObject:[[NSNumber alloc] initWithLong:number]];
      initialSubtraction = (long)(((long)initialSubtraction << 1) + 1);
      [self subtract:number subtractions:shifts initialSubtraction:initialSubtraction currentShiftIteration:currentShiftIteration currentSubtractionIteration:currentSubtractionIteration];
    }
    
    return;
    
  }

  - (void)subtract:(long)number subtractions:(char)subtractions initialSubtraction:(long)initialSubtraction currentShiftIteration:(int)currentShiftIteration currentSubtractionIteration:(int)currentSubtractionIteration
  {
    if (currentSubtractionIteration >= 4) {
      return;
    }
    
    long subtractionValue = initialSubtraction;
    
    for(char b = 0; b < subtractions; b++)  {
      if (currentSubtractionIteration >= 4) {
        return;
      }
      number -= subtractionValue;
      currentSubtractionIteration++;
      subtractionValue = (long)((long)subtractionValue << 1);
      [permutations addObject:[[NSNumber alloc] initWithLong:number]];
      [self shift:number shifts:(subtractions - 1) initialSubtraction:subtractionValue currentShiftIteration:currentShiftIteration currentSubtractionIteration:currentSubtractionIteration];
    }
    
  }

@end

int main(int argc, char const *argv[])
{
  @autoreleasepool {
    Algorithm *myAlgorithm = [[Algorithm alloc] init];
    NSMutableArray *permutations = [myAlgorithm findPermutations];

    printf("[\n");
    for (int i = 0; i < [permutations count]; ++i)
    {
      if (i == ([permutations count] - 1))
      {
        printf("%4d", [[permutations objectAtIndex: i] intValue]);
      }
      else
      {
        printf("%4d, ", [[permutations objectAtIndex: i] intValue]);
      }
    }
    printf("\n]\n");
  }
  return 0;
}