Prim's Algorithm in C producing incorrect output - c

Question

I've been tasked with implementing Prim's algorithm to find the MCST using an adjacency matrix to represent the graph, and a struct to hold the MCST. The program takes in a file input, applies the algorithm and then outputs the minimum cost spanning tree. I got the program to take a file input and produce output, but the values I am getting are incorrect and look like dummy values to me.
My assumption is that the error occurs in either how I am storing the file input in my array, or in the algorithm itself. I've spent a good 12-15 hours troubleshooting this issue and am hoping someone can provide insight. The program is written in C and compiled with make in the format ./a6 <file>. I take and store the file input in my main() and then the methods are used in the order they are called. Below is an example my professor provided. The first line contains info about the vertices being entered and the remaining lines contain the actual data itself.
input:
6 10 0 <<--(size, edges, start)
0 1 16 <<--(from, to, weight)
0 5 21
0 4 19
1 2 5
1 3 6
1 5 11
2 3 10
3 4 18
3 5 14
4 5 33
output:
0 1 16 <<--(first edge)
1 2 5
1 3 6
1 5 11
3 4 18
total cost: 56
My code:
#include <stdio.h>
#include <stdlib.h>
#include <limits.h> /* for INT_MAX */
#define N 10 /* max matrix size is 10 x 10 */
#define INF 9999
int cost = 0;
typedef struct lnode {
int fromv;
int tov;
int weight;
struct lnode *next;
} lnode;
int insertnode(lnode **lst, int from, int to, int wt);
void prims(int amtrx[][N],int n, lnode **lst);
void printpaths(lnode **lst);
void freelist(lnode **lst);
int isValid(int a, int b, int select[]);
int insertnode(lnode **lst, int from, int to, int wt){
lnode *newnode;
newnode = (lnode *) malloc(sizeof(struct lnode));
newnode->fromv = from;
newnode->tov = to;
newnode->weight = wt;
newnode->next=NULL;
if(*lst == NULL){
newnode -> next = *lst;
*lst = newnode;
} else {
lnode *current;
current = *lst;
while(current->next != NULL){
current = current->next;
}
newnode->next = current->next;
current->next = newnode;
}
return 1;
}
int isValid(int a, int b, int select[]){
if(a == b) return 0;
if(select[a] == 0 && select[b] == 0) return 0;
else if (select[a] == 1 && select[b] == 1) return 0;
return 1;
}
void prims(int amtrx[][N], int n, lnode **lst){
int i, j, row, col, edges_seen, min;
int select[N] = {0};
edges_seen = 0;
select[n] = 1;
while(edges_seen < N-1){
min = INF;
row = -1;
col = -1;
for(i = 0; i < N; i++) {
for(j = 0; j < N; j++){
if(amtrx[i][j] < min) {
if(isValid(i, j, select) == 1){
min = amtrx[i][j];
row = i;
col = j;
}
}
}
}
if(row != -1 && col != -1){
select[col] = 1;
select[row] = 1;
cost = cost + min;
insertnode(lst, row, col, min);
edges_seen++;
}
for(i = 0; i < N; i++){
printf("%3d", select[i]);
}
puts("\n\n");
}
}
void printpaths(lnode **lst){
lnode *current;
current = *lst;
while(current != NULL) {
printf("%4i ",current->fromv);
printf("%4i ", current->tov);
printf("%4i \n", current->weight);
current = current->next;
}
printf("\ntotal cost: %4i\n", cost);
}
void freelist(lnode **lst) {
lnode *temp = NULL;
while(*lst != NULL)
{
temp = *lst;
*lst = (*lst)->next;
free(temp);
}
}
int main(int argc, char **argv){
FILE *f = fopen(argv[1], "r");
lnode *lst;
lst = (lnode *)malloc(sizeof(struct lnode));
int i, j, nsz, nedg, fr, to, vtx, wt;
vtx = 1111;
nedg = 999;
nsz = 100;
fscanf(f, "%d %d %d", &nsz, &nedg, &vtx);
int amtrx[nsz][N];
for(i = 0; i < nsz; i++){
for(j = 0; j < nsz; j++){
amtrx[i][j] = INF;
}
}
for(i = 0; i < nedg; i++){
fscanf(f, "%d %d %d", &fr, &to, &wt);
amtrx[fr][to] = wt;
amtrx[to][fr] = wt;
}
fclose(f);
prims(amtrx, vtx, &lst);
printpaths(&lst);
freelist(&lst);
return EXIT_SUCCESS;
}