Find minimum number of wires to connect the bulbs code - c

Question

I have written this C code to find a minimum number of wires required to switch on all the bulbs.
The problem is that there is x number of computers, some of which are On and some are Off and the distance between these bulb from the first bulb is given. The computer can be switched ON by connecting it to its nearby ON the bulb.
So the inputs are as follows:
X = 6 (number of bulbs)
1 0 1 1 0 1(1 means the bulb is ON and 0 means the bulb is OFF)
2 4 8 36 37 40 (distance between one bulb from the first bulb)
and the output will be:
3 (Reason: 4 - 2 = 2, 37 - 36 = 1, 2 + 1 = 3)
#include <stdio.h>
int main(){
int n,pre,post,sum = 0;
scanf("%d",&n);
int arr[n],dist[n];
for(int i =0;i<n;i++){
scanf("%d ",&arr[i]);
}
for(int i =0;i<n;i++){
scanf("%d ",&dist[i]);
}
for(int i =0;i<6;i++){
if(arr[i] == 0){
pre = dist[i]-dist[i-1];
post = dist[i+1]-dist[i];
if(pre>post){
sum +=post;
}
else{
sum+=pre;
}
}
}
printf("\n %d",sum);
}
It keeps on taking the inputs. Please tell me what is the error in this code?
Thanks in advance.
Edited: I missed that scanf("%d",n) by mistake. It was there in my original code and the problem still persists.

Answer 1

As Sandrin mentioned, n is not defined.
Assuming your input file is:
6
1 0 1 1 0 1
2 4 8 36 37 40
You need to add code to set n:
scanf("%d ",&n);
And, you need to insert this before the definitions of your matrix
Here's the refactored code:
#include <stdio.h>
int
main(void)
{
int n, pre, post, sum = 0;
#if 1
scanf("%d ",&n);
#endif
int arr[n], dist[n];
for (int i = 0; i < n; i++)
scanf("%d ", &arr[i]);
for (int i = 0; i < n; i++)
scanf("%d ", &dist[i]);
for (int i = 0; i < 6; i++) {
if (arr[i] == 0) {
pre = dist[i] - dist[i - 1];
post = dist[i + 1] - dist[i];
if (pre > post) {
sum += post;
}
else {
sum += pre;
}
}
}
printf("\n %d", sum);
return 0;
}

Answer 2

Putting a side technical errors (e.g. n not initialized), the algorithms assumes that all problems can be solved by single pass. This is not true for cases like:
1 0 0 0 0 1
0 1 3 4 6 7
Where the code will choose to connect bulbs [0,1], [2,3], and [4,5], based on pre/post distances. However, bulbs 2 and 3 will remain disconnected.
A better algorithm will attempt to find, for each sequence of off bulbs, which is the most expensive connection, and avoid it.

Answer 3

I have come up with this solution for my code and I have tried to consider all the test cases. If you find any test case that won't run feel free to tell.
#include <stdio.h>
#include <stdlib.h>
int main(int ac, char **av){
int n,pre,post,sum = 0;
scanf("%d",&n);
int *input,*distance;
input = malloc(n * sizeof(int));
for (int i=0; i < n; i++)
{
scanf("%d", &input[i]);
}
distance = malloc(n * sizeof(int));
for (int i=0; i < n; i++)
{
scanf("%d", &distance[i]);
}
for(int i =0;i<6;i++){
if(input[i] == 0){
pre = distance[i]-distance[i-1];
if(input[i+1]==1){
post = distance[i+1]-distance[i];
input[i] =1;
if(pre>post){
sum +=post;
}
else{
sum+=pre;
}
}
else{
sum = sum+pre;
}
printf("%d.....%d....%d\n",pre,post,sum); //Debugging
}
}
printf("\n %d",sum);
free(input);
free(distance);
}