Decisions without if statements

Question

Here are the instructions:

/*
 * Write a method called isGameOver. The method should have three parameters, 
 * all integers and in this order: the player's score, the number of lives 
 * the player has remaining, the game level. The method should return true 
 * if the game is over and false otherwise, according to the following game
 * rule. The game continues only when the player has at least one life 
 * remaining and one of these conditions is met: 
 *   --The player is on level 1 and his/her score at least 1000. 
 *   --The player is on level 2 and his/her score at least 2000. 
 *   --The player is on any level and his/her score at least 3000. 
 *   
 * For example, the method call isGameOver(1500, 1, 2) should return true. 
 * 
 * DO NOT USE AN IF STATEMENT

And here is my code:

public static String isGameOver(int score, int lives, int level) {

    while (level == 1 && level < 1001)
        return "false";

    while (level == 2 && level < 2001)
        return "false";

     while (level == 3 && level < 3001)
        return "false";

    return "true";          
}

It's obviously not working, and I just have this feeling it's because I used a while loop. How can I make a decision without using an if statement?

Answer 1

If you want a readable solution, then you can pretty much directly translate the problem description into code.

/**
* The game continues only when the player...
**/
private static boolean gameContinues(int score, int lives, int level) {
    // has at least one life
    boolean stillAlive = lives >= 1; 
    // is on level 1 and his/her score at least 1000
    boolean cond1 = (level == 1 && score >= 1000); 
    // is on level 2 and his/her score at least 2000
    boolean cond2 = (level == 2 && score >= 2000);
    // is on any level and his/her score at least 3000
    boolean cond3 = score >= 3000;

    // return true if has at least one life remaining and one of the conditions is met
    return stillAlive && (cond1 || cond2 || cond3);
}

// The function you want just returns the inverse of what is defined
public static boolean isGameOver(int score, int lives, int level) {
    return !gameContinues(score, lives, level);
}

Answer 2

How about

public static boolean isGameOver(int score, int lives, int level) {
    return lives<1 || (level<3 && score<1000*level) || (score<3000 && level>2);
}

Testing this

isGameOver(900,1,1) // true
isGameOver(1900,1,1) // false
isGameOver(1900,1,2) // true
isGameOver(2900,1,2) // false
isGameOver(3000,1,5) // false
isGameOver(3000,0,5) // true

The three conditions or-ed together will return true if at least one is true. We check in order

1. are we out of lives (lives<1)?
2. did we fail the score conditions for levels 1 and 2 (score conditions are just 1000 points per level)?
3. did we fail the score condition for levels 3 and up (which all have the 3000 points requirement)?

If any of these conditions are true, we return true. Otherwise we return false.