The lazy version

A two-pass solution is fine for warm-up: copy all non-zero values into a new array, then pad with zeros. O(n) time, O(n) memory.

But you can do it in place with O(1) extra memory using two pointers.

In-place, one pass

write points to the next position that should hold a non-zero value. read walks the array. Whenever read lands on a non-zero, swap it into a[write] and advance write.

write = 0
for read in 0..n-1:
    if a[read] != 0:
        swap(a[write], a[read])
        write += 1

Why swap and not just copy? Because we also need to push the zeros that used to be at write somewhere right of read, and a swap does both jobs at once. Order of non-zero values is preserved.

Output

Print the modified array space-separated on one line.