Finding the number of row with the smallest sum of powers, C - c

Question

I have an array, in which I need to find the number of row, which has the smallest sum of powers. Consider the example array:
1 1 1
2 2 2
3 3 3
The first row, (index = 0), the sum of powers is equal to 3 (1^2 + 1^2 + 1^2 = 3).
The second row, (index = 1), the sum of powers is equal to 12 (2^2 + 2^2 + 2^2 = 12).
The third row, (index = 2), the sum of powers is equal to 27 (3^2 + 3^2 + 3^2 = 27).
But my program shows the wrong result - instead of index 0, it shows index 2. What is the problem?
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
int ** alloc(int n, int m)
{
int **array, i;
array = malloc(sizeof(int*) * n);
for(i=0; i<n; i++)
array[i] = malloc(sizeof(int) * m);
return array;
}
void show(int **array, int n, int m)
{
int i,j;
for(i=0; i<n; i++)
{
for(j=0; j<m; j++)
{
printf("%d\t", array[i][j]);
}
printf("\n");
}
}
void fill(int **array, int n, int m, int x)
{
int i,j;
for(i=0; i<n; i++)
{
for(j=0; j<m; j++)
{
array[i][j] = x;
}
}
}
void dealloc(int **array, int n, int m)
{
int i;
for(i=0; i<n; i++)
free(array[i]);
free(array);
}
int smallest_powers_sum(int **array, int n, int m)
{
int sum = 0, minsum = 0, i, j, minindex = -1;
for(i=0; i<n; i++)
{
minsum = sum;
sum = 0;
for(j=0; j<m; j++)
{
sum += pow(array[i][j], 2);
}
if(minsum <= sum)
minindex = i;
printf("sum = %d, minsum = %d, minindex = %d\n", sum, minsum, minindex);
}
return minindex;
}
int main(int argc, char **argv)
{
int **array, n1 = 3, m1 = 3;
array = alloc(n1, m1);
fill(array, n1, m1, 1);
array[0][0] = 1;
array[0][1] = 1;
array[0][2] = 1;
array[1][0] = 2;
array[1][1] = 2;
array[1][2] = 2;
array[2][0] = 3;
array[2][1] = 3;
array[2][2] = 3;
int sum = smallest_powers_sum(array, n1, m1);
printf("index = %d\n", sum);
dealloc(array, n1, m1);
return 0;
}

Answer 1

I think you meant this:
if(sum <= minsum ){
minindex = i;
minsum = sum;
}
Also, initially assign integer_max to minsum.
Here's the code:
int smallest_powers_sum(int **array, int n, int m)
{
int sum = 0, minsum = 1000000, i, j, minindex = -1;
for(i=0; i<n; i++)
{
sum = 0;
for(j=0; j<m; j++)
{
sum += pow(array[i][j], 2);
}
if(sum <= minsum ){
minindex = i;
minsum = sum;
}
printf("sum = %d, minsum = %d, minindex = %d\n", sum, minsum, minindex);
}
return minindex;
}

Answer 2

This line kills all your "memory" of previous rows:
minsum = sum;
You should only update minsum together with updating minindex.
Also your condition for updating minindex seems to be the wrong way around.

Answer 3

This would be one way to do (although a bare-bones version):
#define NROWS 3
#define NCOLS 3
int *getminrow(int *p, int n)
{
int minval = *p;
int *minaddr = p;
while (n >= 1) {
if (*p < minval) {
minval = *p;
minaddr = p;
}
n--;
p++;
}
return minaddr;
}
int sumrow(int *p, int n)
{
int sum = 0;
while (n >= 1) {
sum += (*p);
n--;
p++;
}
return sum;
}
int main(void)
{
int *array = malloc(NROWS * NCOLS);
int listsum[NROWS];
int i, j;
array[0 * NROWS + 0] = 1;
array[0 * NROWS + 1] = 1;
array[0 * NROWS + 2] = 1;
array[1 * NROWS + 0] = 2;
array[1 * NROWS + 1] = 2;
array[1 * NROWS + 2] = 2;
array[2 * NROWS + 0] = 3;
array[2 * NROWS + 1] = 3;
array[2 * NROWS + 2] = 3;
for (i = 0; i < NROWS; i++) {
for (j = 0; j < NCOLS; j++) {
array[i * NROWS + j] = pow(array[i * NROWS + j], 2);
}
}
for (i = 0; i < NROWS; i++)
listsum[i] = sumrow(&array[i], NCOLS);
printf("Min row: %d\n", getminrow(listsum, NROWS) - listsum);
return 0;
}

Answer 4

I think there are some problem in your logic. First "if(minisum<=sum)". It must be "if(sum<=minisum)". Second, if you're just using coding like that, then the condition will be considered only condition i and i-1. So, my advice to change the syntax "if(minisum<=sum)" with the following script. (There are new variables that I call minisumtemp).
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
int ** alloc(int n, int m)
{
int **array, i;
array = malloc(sizeof(int*) * n);
for(i=0; i<n; i++)
array[i] = malloc(sizeof(int) * m);
return array;
}
void show(int **array, int n, int m)
{
int i,j;
for(i=0; i<n; i++)
{
for(j=0; j<m; j++)
{
printf("%d\t", array[i][j]);
}
printf("\n");
}
}
void fill(int **array, int n, int m, int x)
{
int i,j;
for(i=0; i<n; i++)
{
for(j=0; j<m; j++)
{
array[i][j] = x;
}
}
}
void dealloc(int **array, int n, int m)
{
int i;
for(i=0; i<n; i++)
free(array[i]);
free(array);
}
int smallest_powers_sum(int **array, int n, int m)
{
//int sum = 0, minsum = 0, i, j, minindex = -1;
int sum = 0, minsum = 0, i, j, minindex = 0, minsumtemp; // add new variable : minsumtemp
for(i=0; i<n; i++)
{
minsum = sum;
sum = 0;
for(j=0; j<m; j++)
{
sum += pow(array[i][j], 2);
}
//if(minsum <= sum) this the problem
// minindex = i;
if (i==0) minsumtemp = sum; // initialized first value for minsumtep
if (sum<=minsumtemp)
{
minindex = i;
minsumtemp = sum;
}
printf("sum = %d, minsum = %d, minindex = %d\n", sum, minsum, minindex);
}
return minindex;
}
int main(int argc, char **argv)
{
int **array, n1 = 3, m1 = 3;
array = alloc(n1, m1);
fill(array, n1, m1, 1);
array[0][0] = 1;
array[0][1] = 1;
array[0][2] = 1;
array[1][0] = 2;
array[1][1] = 2;
array[1][2] = 2;
array[2][0] = 3;
array[2][1] = 3;
array[2][2] = 3;
int sum = smallest_powers_sum(array, n1, m1);
printf("index = %d\n", sum);
dealloc(array, n1, m1);
return 0;
}