How do you write an algorithm for the multiplication of two matrix [2D array]?

Problem statement:
Given two matrices, the task is to multiply them. Matrices can either be square or rectangular.
Example:
Input: int m1[][] = {{2, 3, 4}, {5, 6, 7}}; // 2 X 3 matrix
int m2[][] = {{1, 2}, {3, 4}, {5, 6}}; // 3 X 2 matrix
Output: {{31, 40},{58,76}}

1. public class MatrixMultiplication {
2.     public static void main(String args[]) {
3.         int m1[][] = {{2, 3, 4}, {5, 6, 7}};    // 2 X 3 matrix
4.         int m2[][] = {{1, 2}, {3, 4}, {5, 6}};  // 3 X 2 matrix
5.         int res[][] = new int[2][2];    // resultant matrix of 2 X 2
6.         for (int i = 0; i < 2; i++) {   // i represent row
7.             for (int j = 0; j < 2; j++) {   // j represent column
8.                 res[i][j] = 0;  // assume res[0][0] = 0
9.                 for (int k = 0; k < 3; k++) {
10.                     // k represent first matrix i.e. m1 -> number of column for                        // counter sum
11.                     res[i][j] = res[i][j] + m1[i][k] * m2[k][j];
12.                 }
13.             }
14.         }
15.         // printing the resultant matrix
16.         for (int i = 0; i < 2; i++) {
17.             for (int j = 0; j < 2; j++) {
18.                 System.out.print(res[i][j] + " ");
19.             }
20.             System.out.println();
21.         }
22.     }
23. }

Method-II:

1. public class MatrixMultiplication2D {
2.     public static void main(String args[]) {
3.         int m1[][] = {{2, 3, 4}, {5, 6, 7}};    // 2 X 3 matrix
4.         int m2[][] = {{1, 2}, {3, 4}, {5, 6}};  // 3 X 2 matrix
5.         int sum = 0;    // initial sum value is 0
6.         int res[][] = new int[2][2];    // resultant matrix of 2 X 2
7.         for (int i = 0; i < 2; i++) {   // i represent row
8.             for (int j = 0; j < 2; j++) {   // j represent column
9.                 res[i][j] = 0;  // assume res[0][0] = 0
10.                 for (int k = 0; k < 3; k++) {
11.                     // k represent first matrix i.e. m1 -> number of column for                        // counter sum
12.                     sum = sum + m1[i][k] * m2[k][j];
13.                 }
14.                 res[i][j] = sum;    //  assigned sum value to resultant matrix
15.                 sum = 0;    // reset to 0 for next iteration
16.             }
17.         }
18.         // printing the resultant matrix
19.         for (int i = 0; i < 2; i++) {
20.             for (int j = 0; j < 2; j++) {
21.                 System.out.print(res[i][j] + " ");
22.             }
23.             System.out.println();
24.         }
25.     }
26. }

Output:

31 40

58 76

How do you print all elements of a matrix in diagonal order?

1. public class PrintDiagonalMatrix
2. {
3.   static final int ROW = 5;
4.   static final int COL = 4;
5.   // min of two numbers
6.   static int min(int a, int b)
7.   {
8.     return (a < b) ? a : b;
9.   }
10.   // min of three numbers
11.   static int min(int a, int b, int c)
12.   {
13.     return min(min(a, b), c);
14.   }
15.   // max of two numbers
16.   static int max(int a, int b)
17.   {
18.     return (a > b) ? a : b;
19.   }
20.   // print matrix in diagonal order
21.   static void diagonalOrder(int matrix[][])
22.   {
23.     for (int line = 1; line <= (ROW + COL - 1); line++)
24.     {
25.       int start_col = max(0, line - ROW);
26.       int count = min(line, (COL - start_col), ROW);
27.       for (int j = 0; j < count; j++)
28.         System.out.print(matrix[min(ROW, line) - j - 1][start_col + j] + " ");
29.       System.out.println();
30.     }
31.   }
32.   // print a matrix
33.   static void printMatrix(int matrix[][])
34.   {
35.     for (int i = 0; i < ROW; i++)
36.     {
37.       for (int j = 0; j < COL; j++)
38.         System.out.print(matrix[i][j] + " ");
39.       System.out.print("\n");
40.     }
41.   }
42.   public static void main(String[] args)
43.   {
44.     int M[][] =
45.     {
46.         { 1, 2, 3, 4 },
47.         { 5, 6, 7, 8 },
48.         { 9, 10, 11, 12 },
49.         { 13, 14, 15, 16 },
50.         { 17, 18, 19, 20 }, };
51.     System.out.print("Given matrix is \n");
52.     printMatrix(M);
53.     System.out.print("\nDiagonal printing of matrix is \n");
54.     diagonalOrder(M);
55.   }
56. }

Output:
Given matrix is
1 2 3 4
5 6 7 8
9 10 11 12
13 14 15 16
17 18 19 20

Diagonal printing of matrix is
1
5 2
9 6 3
13 10 7 4
17 14 11 8
18 15 12
19 16
20 

How do you print all elements of a matrix in diagonal order?

Problem statement: 

Print Matrix Diagonally (Diagonal order)