Square Matrix Multiply Recursive in Java using Divide and Conquer?

Question

I have a school project to create 2 versions of a javacode that multiplies two square matrices. To make it easier, they only have to work for 2x2, 4x4, 8x8 etc. We have a pseudo

Answer 1

here is a Java implementation without coping the matrices. This works only for nxn matrices so that n= 2^x.

public static int[][] matrixMultiplicationFinal(int[][] A, int[][] B){

    return  matrixMultiplication(
            A, B, 0, 0, 
            0,0, A.length);

}


public static int[][] matrixMultiplication(
        int[][] A, int[][] B, int rowA, int colA, 
        int rowB, int colB, int size){

    int[][] C= new int[size][size];

    if(size==1)
        C[0][0]= A[rowA][colA]*B[rowB][colB];

    else{

        int newSize= size/2;
        //C11
         sumMatrix(C, 

            matrixMultiplication(A, B, rowA, colA, rowB, colB, newSize),
            matrixMultiplication(A, B, rowA, colA+newSize, rowB+ newSize, colB, newSize),
        0, 0);

         sumMatrix(C, 

            matrixMultiplication(A, B, rowA, colA, rowB, colB + newSize, newSize),
            matrixMultiplication(A, B, rowA, colA+newSize, rowB+ newSize, colB+newSize, newSize),
        0, newSize);

         sumMatrix(C, 

            matrixMultiplication(A, B, rowA+ newSize, colA, rowB, colB, newSize),
            matrixMultiplication(A, B, rowA+ newSize, colA+newSize, rowB+ newSize, colB, newSize),
        newSize, 0);

         sumMatrix(C, 

            matrixMultiplication(A, B, rowA+ newSize, colA, rowB, colB+newSize, newSize),
            matrixMultiplication(A, B, rowA+ newSize, colA+newSize, rowB+ newSize, colB+newSize, newSize),
        newSize, newSize);
    }

    return C;

}


private static void sumMatrix(int[][] C, int[][]A, int[][]B,int rowC, int colC){
    int n=A.length;
    for(int i =0; i