如何编写一个可以轻松维护的概率算法？

Question

假设我想创造一个游戏.在游戏开始时,玩家将挑选一个怪物.

公平地挑选怪物很容易.

// get all monsters with equal chance
public Monster getMonsterFair(){
    Monster[] monsters = {new GoldMonster(), new SilverMonster(), new BronzeMonster()};
    int winIndex = random.nextInt(monsters.length);
    return monsters[winIndex];
}

并不公平地挑选怪物.

// get monsters with unequal chance
public Monster getMonsterUnFair(){
    double r = Math.random();
    // about 10% to win the gold one
    if (r < 0.1){
        return new GoldMonster();
    }
    // about 30% to winthe silver one
    else if ( r < 0.1 + 0.2){
        return new SilverMonster();
    }
    // about 70% to win the bronze one
    else {
        return new BronzeMonster();
    }   
}

问题是,当我在游戏中添加一个新怪物时,我必须编辑if-else.或者我将赢得GoldMonster的机会改为0.2,我必须将所有0.1改为0.2.它很难看,而且不容易维护.

// get monsters with unequal change & special monster
public Monster getMonsterSpecial(){
    double r = Math.random();
    // about 10% to win the gold one
    if (r < 0.1){
        return new GoldMonster();
    }
    // about 30% to win the silver one
    else if ( r < 0.1 + 0.2){
        return new SilverMonster();
    }
    // about 50% to win the special one
    else if ( r < 0.1 + 0.2 + 0.2){
        return new SpecialMonster();
    }
    // about 50% to win the bronze one
    else {
        return new BronzeMonster();
    }
}

如何重构这种概率算法,以便在添加新怪物并调整获胜怪物的机会时可以轻松维护代码？

Answer 1

基本上就是@Egor Skriptunoff 所说的。这应该很容易扩展。如果您Class<Monster>不想使用enum.

enum Monster {
    GOLD(1),
    SILVER(3),
    BRONZE(6) // pseudo probabilities

    private int weight;
    // constructor etc..
}

public Monster getMonsterSpecial() {
    List<Monster> monsters = new ArrayList<>();

    for(Monster monsterType : Monster.values()) {
        monsters.addAll(Collections.nCopies(monsterType.getWeight(), monsterType)); 
    }

    int winIndex = random.nextInt(monsters.length);
    return monsters.get(winIndex);
}

如果您仍然想实例化怪物类，您也许可以将枚举设为复数Monsters，并让它指向 a 。Class<? extends Monster>我只是想让这个例子更清楚。