Why does both of these codes work when the syntax are written differently?

Question

https://code.sololearn.com/ce6DL5nk3htF/?ref=app
https://code.sololearn.com/cLiD6yoe1tej/?ref=app

Answer 1

https://code.sololearn.com/c8qHF4qisvZC/?ref=app
https://code.sololearn.com/cRB6vU0Pbt9Q/?ref=app

These codes. Is the return 0; not necessary?