从小到大排序

1.用OC外层封装的方法

-(NSArray *)combine:(NSArray * )array count:(NSInteger)count{
    int arr[array.count];
    for (int i = 0; i < array.count; i++)
    {
        arr[i] = [array[i] intValue];
    }
    int num = count;
    int result[num];
    
    return combine_increase(arr, 0, result, num, num, sizeof(arr)/sizeof(int));
}

2.用C语言和OC混编实现的方法，直接把结果返回

//arr为原始数组
//start为遍历起始位置
//result保存结果，为一维数组
//count为result数组的索引值，起辅助作用
//NUM为要选取的元素个数
//arr_len为原始数组的长度，为定值
NSArray * combine_increase(int* arr, int start, int* result, int count, const int NUM, const int arr_len)
{
    NSMutableArray * resultArr = [NSMutableArray array];
    int i = 0;
    for (i = start; i < arr_len + 1 - count; i++)
    {
        result[count - 1] = i;
        if (count - 1 == 0)
        {
            int j;
            NSMutableArray * subArr = [[NSMutableArray alloc]init];
            for (j = NUM - 1; j >= 0; j--){
                [subArr addObject:[NSNumber numberWithInt:arr[result[j]]]];
//                printf("%d\t",arr[result[j]]);
            }
            [resultArr addObject:subArr];
//            printf("\n");
        }
        else
         [resultArr addObjectsFromArray:combine_increase(arr, i + 1, result, count - 1, NUM, arr_len)];
    }
    return resultArr;
}

3.纯C语言实现

//arr为原始数组
//start为遍历起始位置
//result保存结果，为一维数组
//count为result数组的索引值，起辅助作用
//NUM为要选取的元素个数
//arr_len为原始数组的长度，为定值
void combine_increase(int* arr, int start, int* result, int count, const int NUM, const int arr_len)
{
    int i = 0;
    for (i = start; i < arr_len + 1 - count; i++)
    {
        result[count - 1] = i;
        if (count - 1 == 0)
        {
            int j;
            for (j = NUM - 1; j >= 0; j--)
                printf("%d\t",arr[result[j]]);
            printf("\n");
        }
        else
            combine_increase(arr, i + 1, result, count - 1, NUM, arr_len);
    }
}

从大到小排序

1.用OC外层封装的方法

-(NSArray *)combine2:(NSArray * )array count:(int)count{
    int arr[array.count];
    int i;
    for (i = 0; i < array.count; i++)
    {
        arr[i] = [array[i] intValue];
    }
    int result[count];
    
    return combine_decrease(arr,i, result, count, count);
}

2.用C语言和OC混编实现的方法，直接把结果返回

//arr为原始数组
//start为遍历起始位置
//result保存结果，为一维数组
//count为result数组的索引值，起辅助作用
//NUM为要选取的元素个数
NSArray * combine_decrease(int* arr, int start, int* result, int count, const int NUM)
{
    NSMutableArray * resultArr = [NSMutableArray array];
    int i;
    for (i = start; i >=count; i--)
    {
        result[count - 1] = i - 1;
        if (count > 1)
        {
            [resultArr addObjectsFromArray:combine_decrease(arr, i - 1, result, count - 1, NUM)];
        }
        else
        {
            int j;
            NSMutableArray * subArr = [[NSMutableArray alloc]init];
            for (j = NUM - 1; j >=0; j--){
                [subArr addObject:[NSNumber numberWithInt:arr[result[j]]]];
//                printf("%d\t",arr[result[j]]);
            }
            [resultArr addObject:subArr];
//            printf("\n");
        }
    }
    return resultArr;
}

3.纯C语言实现

//arr为原始数组
//start为遍历起始位置
//result保存结果，为一维数组
//count为result数组的索引值，起辅助作用
//NUM为要选取的元素个数
void combine_decrease(int* arr, int start, int* result, int count, const int NUM)
{
  int i;
  for (i = start; i >=count; i--)
  {
    result[count - 1] = i - 1;
    if (count > 1)
    {
      combine_decrease(arr, i - 1, result, count - 1, NUM);
    }
    else
    {
      int j;
      for (j = NUM - 1; j >=0; j--)
    printf("%d\t",arr[result[j]]);
      printf("\n");
    }
  }
}