How to print all square submatrices of square matrix in C? - c

Question

Please, help me to find and print all square submatrices of square matrix from big to small square matrices in C programming language
I wrote code that works wrong:
int main() {
int mtrx_size = 8;
int mat[8][8] = {
{ 1, 2, 3, 4, 5, 6, 7, 8},
{ 9,10,11,12,13,14,15,16},
{17,18,19,20,21,22,23,24},
{25,26,27,28,29,30,31,32},
{33,34,35,36,37,38,39,40},
{41,42,43,44,45,46,47,48},
{49,50,51,52,53,54,55,56},
{57,58,59,60,61,62,63,64}
};
int i,j;
int sub_mtrx_size;
for(sub_mtrx_size = mtrx_size; sub_mtrx_size > 1 ; sub_mtrx_size--)
{
for(i = 0; i < sub_mtrx_size; i++)
{
for(j = 0; j < sub_mtrx_size; j++)
{
printf("%3d ", mat[i][j]);
}
printf("\n");
}
printf("\n");
}
return 0;
Here I need to find all 8x8, 7x7, 6x6, 5x5, 4x4, 3x3 and 2x2 submatrices.

Answer 1

Your code was just printing a single sub-matrix for each size, positioned in the upper-left corner of the matrix. You need to add i and j offsets to get the sub-matrices at all positions:
#include <stdio.h>
int main() {
int mtrx_size = 8;
int mat[8][8] = {
{ 1, 2, 3, 4, 5, 6, 7, 8},
{ 9,10,11,12,13,14,15,16},
{17,18,19,20,21,22,23,24},
{25,26,27,28,29,30,31,32},
{33,34,35,36,37,38,39,40},
{41,42,43,44,45,46,47,48},
{49,50,51,52,53,54,55,56},
{57,58,59,60,61,62,63,64}
};
int i, j, ioff, joff, off_cnt;
int sub_mtrx_size;
for(sub_mtrx_size = mtrx_size; sub_mtrx_size > 1 ; sub_mtrx_size--) {
off_cnt = mtrx_size - sub_mtrx_size + 1;
for (ioff = 0; ioff < off_cnt; ioff++) {
for (joff = 0; joff < off_cnt; joff++) {
for (i = 0; i < sub_mtrx_size; i++) {
for (j = 0; j < sub_mtrx_size; j++) {
printf("%3d ", mat[i+ioff][j+joff]);
}
printf("\n");
}
printf("\n");
}
}
}
return 0;
}

Answer 2

Java implementation for a general nxm matrix:
private static void printSubMatrix(int[][] mat) {
int rows=mat.length;
int cols=mat[0].length;
//prints all submatrix greater than or equal to 2x2
for (int subRow = rows; subRow >= 2; subRow--) {
int rowLimit = rows - subRow + 1;
for (int subCol = cols; subCol >= 2; subCol--) {
int colLimit = cols - subCol + 1;
for (int startRow = 0; startRow < rowLimit; startRow++) {
for (int startCol = 0; startCol < colLimit; startCol++) {
for (int i = 0; i < subRow; i++) {
for (int j = 0; j < subCol; j++) {
System.out.print(mat[i + startRow][j + startCol] + " ");
}
System.out.print("\n");
}
System.out.print("\n");
}
}
}
}
}

Answer 3

#include <stdio.h>
int main() {
int mtrx_size = 8;
int mat[8][8] = {
{ 1, 2, 3, 4, 5, 6, 7, 8},
{ 9,10,11,12,13,14,15,16},
{17,18,19,20,21,22,23,24},
{25,26,27,28,29,30,31,32},
{33,34,35,36,37,38,39,40},
{41,42,43,44,45,46,47,48},
{49,50,51,52,53,54,55,56},
{57,58,59,60,61,62,63,64}
};
int i, j, ioff, joff, off_cnt;
int sub_mtrx_size;
/* if we make terminating condition sub_mtrx_size>=1 then we will have all
possible square sub matrices */
for(sub_mtrx_size = mtrx_size; sub_mtrx_size >= 1 ; sub_mtrx_size--) {
off_cnt = mtrx_size - sub_mtrx_size + 1;
for (ioff = 0; ioff < off_cnt; ioff++) {
for (joff = 0; joff < off_cnt; joff++) {
for (i = 0; i < sub_mtrx_size; i++) {
for (j = 0; j < sub_mtrx_size; j++) {
printf("%3d ", mat[i+ioff][j+joff]);
}
printf("\n");
}
printf("\n");
}
}
}
return 0;
}