Optimize code to get following output in c - c

Question

I had an interview last week. They asked me to write a code to print like this
input :5
0
101
21012
3210123
432101234
54321012345
i wrote the below code but he said i could optimize this more . i cant figure it out.
,
int main(){
int n,i,j,k,lim,num;
scanf("%d",&n);//getting input starting number of last row
lim=n;
int collen=n+2;//it denotes end of row
for(i=0;i<n+1;i++)
{
num=i;
k=0;
for(j=0;j<collen-1;j++){
if(j<lim)
printf(" ");
else if(num<0){
printf("%d",++k);
}
else{
printf("%d",num--);
}
}//j for
printf("\n");
collen++;
lim--;
}//i for
}// main end
I have different code at first attempt, I used flag to detect when num reaches for incrementing and decrementing, it was complex there was about 4 if inside second loop, so I optimized that code to the above one. He said can you optimize more? I have no idea to optimize it .
My question: can it be optimized? If it can be - please post the code

Answer 1

There are more for-loops than those comparing by <. for(i=0;i<n+1;i++) is much clearer written as for (i = 0; i <= n; i++).
If you initialize a value, in example int collen=n+2;, and later use it like collen-1, save the subtraction and initialize it adjusted.
Separate this complex inner loop with ifs into their own loops.
Use less variables.
Use more and consistent whitespace.
And now my solution, but as yours it can only handle inputs from 0 to 9:
#include <stdio.h>
#include <stdlib.h>
int main(void) {
int n;
printf("input :");
if (scanf("%d", &n) != 1 || n < 0 || n > 9) {
printf("input not recognized or invalid\n");
return EXIT_FAILURE;
}
for (int i = 0; i <= n; ++i) {
printf("%*d", n - i + 1, i);
for (int j = i - 1; j >= 0; --j) {
printf("%d", j);
}
for (int j = 1; j <= i; ++j) {
printf("%d", j);
}
printf("\n");
}
return EXIT_SUCCESS;
}

Answer 2

This looks optimized to the brims:
int main( int argc, char **argv )
{
puts( "input :5");
puts( " 0");
puts( " 101");
puts( " 21012");
puts( " 3210123");
puts( " 432101234");
puts( "54321012345");
}

Answer 3

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
/* Print a pyramid */
int
main(int argc, char **argv)
{
int size = argc > 1 ? strtol(argv[1],NULL,10) : 5;
if( size > 9 || size < 0) {
fprintf(stderr, "Invalid size\n");
return EXIT_FAILURE;
}
for(int line = 0; line <= size; line++) {
char template[]="9876543210123456789";
char *s = template + 9 - size;
template[10 + line] = '\0';
memset(s, ' ', size - line);
if(puts(s) == EOF) {
perror("puts");
return EXIT_FAILURE;
}
}
return EXIT_SUCCESS;
}