[Nero_3D]

That would be the faster solution with a little bit of memory usage

pawn Код:

CMD:respawncars(playerid, unused[]) {
    #pragma unused unused

    new
        i,
        bool: vUsed[MAX_VEHICLES + 1]
    ;
    foreachex(Player, i) {
        vUsed[GetPlayerVehicleID(i)] = true;
    }
    for(i = 1; i <= MAX_VEHICLES; ++i) {
        if(!vUsed[i]) {
            DestroyVehicle(i);
        }
    }
    return true;
}