Third smallest number in matrices and its addition

Question

Hi, How can i addition one + one matric (array data structure) and after it find the third smallest number in it in C language (not C++)? Thank you for the code.

Answer 1

• First decide how to represent the matrix (hint: use an array of arrays)
• Then figure out how to add two matrices - this is simple
• Then, how do you find the 3rd smallest element in a sequence? There are many ways! Is efficiency especially important for you? What algorithmic complexity is required?

Answer 2

If you are trying to access SIMD instructions, I don't believe there is an approach that will do both at the same time. If you are not trying to do use SIMD, then just keep a temp array of the three smallest values (like a priority queue) that is updated each time a sum is computed in the matrix.

If this were C++, the priority queue could be kept in a functor object used by the STL algorithms.

Answer 3

Example code follows:

void addMatrix(unsigned int size, double const * const a, double const * const  b, double * const res) {
   int i;
   for (i = 0; i < size * size; ++i)
       res[i] = a[i] + b[i];
}

double findThirdSmallest(unsigned int size, double const * const input) {
   //save the three smallest values inside res
   double res[3];
   int i;
   for (i = 0; i < 3; ++i) {
       res[i] = LDBL_MAX;
   }
   for (i = 0; i < size * size; ++i) {
       int j;
       for (j = 0; j < 3; ++j) {
           if (input[i] < res[j]) {
               int k;
               for (k = 2; k != j; --k) {
                   res[k] = res[k - 1];
               }
               res[j] = input[i];
               break;
           }
       }
   }
   return res[2];
}

EDIT: Changing the type and the size of the matrix will be your work.