Monday, August 2, 2010

Gambler.java

/*************************************************************************
* Compilation: javac Gambler.java
* Execution: java Gambler stake goal N
*
* Simulates a gambler who start with $stake and place fair $1 bets
* until she goes broke or reach $goal. Keeps track of the number of
* times she wins and the number of bets she makes. Run the experiment N
* times, averages the results, and prints them out.
*
* % java Gambler 50 250 1000
* Percent of games won = 19.0
* Avg # bets = 9676.302
*
* % java Gambler 50 150 1000
* Percent of games won = 31.9
* Avg # bets = 4912.13
*
* % java Gambler 50 100 1000
* Percent of games won = 49.6
* Avg # bets = 2652.352
*
*************************************************************************/

public class Gambler {

public static void main(String[] args) {
int stake = Integer.parseInt(args[0]); // gambler's stating bankroll
int goal = Integer.parseInt(args[1]); // gambler's desired bankroll
int T = Integer.parseInt(args[2]); // number of trials to perform

int bets = 0; // total number of bets made
int wins = 0; // total number of games won

// repeat N times
for (int t = 0; t < T; t++) {

// do one gambler's ruin simulation
int cash = stake;
while (cash > 0 && cash < goal) {
bets++;
if (Math.random() < 0.5) cash++; // win $1
else cash--; // lose $1
}
if (cash == goal) wins++; // did gambler go achieve desired goal?
}

// print results
System.out.println(wins + " wins of " + T);
System.out.println("Percent of games won = " + 100.0 * wins / T);
System.out.println("Avg # bets = " + 1.0 * bets / T);
}

}

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