array2.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

static void sumSubArraysFast(int* arr, size_t size){
	int i,j,k;
	int matsize = size * size;
	int matsizebytes = sizeof(int) * matsize;
	int* mat = malloc(matsizebytes);
	memset(mat, 0, matsizebytes);
	memcpy(mat, arr, size*sizeof(int));

	for(i = 1; i < size; i++){
		int len = i+1;
		for(j = 0; j < (size - (len - 1)); j++){
			mat[j + i*size] = mat[j + (i-1)*size] + mat[i+j];
		}
	}

	//print
	for(i = 0; i < size; i++){
		for(j = 0; j < size; j++){
			printf("%4d ", mat[j + i*size]);
		}
		printf("\n");
	}
}

int main()
{
	int arr[] = { 11,23,36,43,56,63,71,89,93,10 };
	printf("slow\n");
	sumSubArrays(arr, 10);
	printf("fast\n");
	sumSubArraysFast(arr, 10);
	return 0;
}