Multiple pointers is key.
Because we don't need or care about what is in the array after non-zero elements, we can simply keep a separate pointer of where to start the zeros. This extra pointer will prevent us from having to store a separate temp array, with the intuition being that we know what we need to fill after (exclusively 0s!).
Despite having two loops, the time complexity simplifies to O(n). However, the space complexity is constant since we're using the same array.
Follow the below illustration for more guidance:
