I'm going through the Programming With a Purpose course on Coursera, and trying to come up with my own implementation of some of the example programs before looking at the example. I just finished the example of a gambling situation. I was hoping to get some more eyes on my code and be told whether my version is going to behave differently from the example. Due to the nature of simulations, I can't just compare the output of the two, since it will vary.
This is the explanation of what the code is meant to represent:
Gambler (PROGRAM 1.3.8) is a simulation that can help answer these ques tions. It does a sequence of trials, using Math.random() to simulate the sequence of bets, continuing until the gambler is broke or the goal is reached, and keeping track of the number of wins and the number of bets.
Mine:
public class Gambler
{
public static void main(String[] args)
{
int stake = Integer.parseInt(args[0]);
int initialStake = stake;
int goal = Integer.parseInt(args[1]);
int desiredGain = goal - stake;
int trials = Integer.parseInt(args[2]);
int games = 0;
int wins = 0;
int bets = 0;
while (games < trials)
{
bets++;
if (Math.random() >= 0.5)
{
stake++;
desiredGain = goal - stake;
if (desiredGain <= 0)
{
wins++;
games++;
stake = initialStake;
}
}
else
{
stake--;
if (stake < 1)
{
games++;
stake = initialStake;
}
}
}
int averageBets = bets / trials;
int percentWins = (100*wins / trials);
System.out.println("Theoretical chance of winning: " + 100*initialStake/goal);
System.out.println("Expected Bets: " + initialStake*(goal - initialStake));
System.out.println(percentWins + "% wins");
System.out.println("Average # bets: " + averageBets);
}
}
Example:
public class Gambler2
{
public static void main(String[] args)
{
int stake = Integer.parseInt(args[0]);
int goal = Integer.parseInt(args[1]);
int T = Integer.parseInt(args[2]);
int bets = 0;
int wins = 0;
for (int t=0; t<T; t++)
{
int cash = stake;
while (cash > 0 && cash < goal)
{
bets++;
if (Math.random() < 0.5) cash++;
else cash--;
}
if (cash == goal) wins++;
}
int averageBets = bets / T;
int percentWins = (100*wins / T);
System.out.println("Theoretical chance of winning: " + 100*stake/goal);
System.out.println("Expected Bets: " + stake*(goal - stake));
System.out.println(percentWins + "% wins");
System.out.println("Average # bets: " + averageBets);
}
}
The example is obviously much cleaner, but here is why I think mine should work the same:
- Each time the player's current stake exceeds the goal or reaches 0, the number of games played is incremented. When games == trials, the loop ends.
- When a game ends, stake is reset to its initial value for the next trial
- Bets is incremented each time the loop runs
- If the current stake meets or exceeds the goal, wins is incremented
I set up my conditions for interpreting the output of Math.random() opposite of the example. If that even makes a difference at all, it seems like it would take a lot more than 1000 trials before it became apparent.
I just want to make sure I'm not missing something.
I'm really proud of my solution to part 2. When I first read it, I was freaking stumped, I had no idea how to approach it. I was wondering if I was going to wind up resorting to brute forcing it in factorial time. But then I had an idea on the way home, and I one shotted it! (Got a few tests on the example but first try on the actual input)
Part 1 for completeness: