"Enlarging" a 2D array by factor (m,n) [closed] - c++

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Say I have a 2D array of size h1 x w1
I want to enlarge it (Just like we enlarge an image) by a factor m,n
So that my resulting array if of the size h1*m , w1*n
for example, I have an array arr1[2][2] of size (2, 2)
01 11
Now I enlarged it by a factor (3, 3) so my new array arr2[6][6] becomes
000111
000111
000111
111111
111111
111111
Can you suggest me an algorithm / iterative loop which could generate arr2 by given information ?

Answer 1

I use pointers to arrays in a smart way to index continuous memory as 2d array and a declarator for VLA in a function prototype.
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <stdint.h>
#define ARRAY_SIZE(x) (sizeof(x)/sizeof(x[0]))
#define ERR_ON(expr, msg, ...) \
do{ if(expr) { fprintf(stderr, "%d: error %s failed: " msg "\n", __LINE__, #expr, ##__VA_ARGS__); exit(-1); } }while(0)
/**
* Input: array p with x columns and y rows
* Output: int arr[y * factory][x * factorx]
* newly allocated array created from p resized by a factorx and factory
*/
void *arr2d_getenlarged(size_t x, size_t y, int p[y][x], size_t factorx, size_t factory)
{
const size_t newx = x * factorx;
const size_t newy = y * factory;
int (* const ret)[newx] = malloc(sizeof(*p) * newx * newy);
ERR_ON(ret == NULL, "");
for (size_t i = 0; i < x; ++i) {
for (size_t j = 0; j < y; ++j) {
const int val = p[i][j];
for (size_t m = 0; m < factorx; ++m) {
for (size_t n = 0; n < factory; ++n) {
ret[i * factorx + m][j * factory + n] = val;
}
}
}
}
return ret;
}
void arr2d_print(size_t x, size_t y, int (*arr)[x])
{
printf("--- %p ---\n", (void*)arr);
for (size_t i = 0; i < x; ++i) {
for (size_t j = 0; j < y; ++j) {
printf("[%d,%d]=%d ", i, j, arr[i][j]);
}
printf("\n");
}
}
int main()
{
int (*arr)[2] = malloc(sizeof(*arr) * 2);
ERR_ON(arr == NULL, "");
memcpy(arr, (int[2][2]){{0,1},{1,1}}, sizeof((int[2][2]){0}));
arr2d_print(2, 2, arr);
int (*arr3)[6] = (void*)arr2d_getenlarged(2, 2, &arr[0][0], 3, 3);
arr2d_print(6, 6, arr3);
free(arr);
free(arr3);
printf("Hello World");
return 0;
}
Example output:
--- 0x1203010 ---
[0,0]=0 [0,1]=1
[1,0]=1 [1,1]=1
--- 0x1203030 ---
[0,0]=0 [0,1]=0 [0,2]=0 [0,3]=1 [0,4]=1 [0,5]=1
[1,0]=0 [1,1]=0 [1,2]=0 [1,3]=1 [1,4]=1 [1,5]=1
[2,0]=0 [2,1]=0 [2,2]=0 [2,3]=1 [2,4]=1 [2,5]=1
[3,0]=1 [3,1]=1 [3,2]=1 [3,3]=1 [3,4]=1 [3,5]=1
[4,0]=1 [4,1]=1 [4,2]=1 [4,3]=1 [4,4]=1 [4,5]=1
[5,0]=1 [5,1]=1 [5,2]=1 [5,3]=1 [5,4]=1 [5,5]=1
Hello World
Live version available at onlinegdb.

Answer 2

#include <stdio.h>
#include <stdlib.h>
#define ENLARGEX 3
int src[2][2] = {{0,1},{1,1}};
int main(int argc, const char * argv[]) {
// insert code here...
int **dest;
//int dest[6][6] ={0,};
int i, j;
int sizesrc = sizeof(src)/sizeof(int)/2;
dest = (int **)malloc(sizeof(int*)*sizesrc*ENLARGEX);
for (i = 0; i < sizesrc*ENLARGEX; i++) {
dest[i] = (int *)malloc(sizeof(int)*sizesrc*ENLARGEX);
}
for (i = 0; i < sizesrc*ENLARGEX; i++){
for(j = 0; j < sizesrc*ENLARGEX; j++) {
dest[i][j] = src[i/ENLARGEX][j/ENLARGEX];
printf("%d ", dest[i][j]);
}
printf("\n");
}
for (i = 0; i < sizesrc*ENLARGEX; i++) {
free(dest[i]);
}
free(dest);
return 0;
}