在java中，如何替换ArrayList中的重复数字？ [重复]

Possible Duplicate:
How do I remove repeated elements from ArrayList?

可能重复:如何从ArrayList中删除重复的元素?

I want to replace a duplicate number (if any) that i store in an ArrayList. I obtianed the numbers for a Random variable. Here is the class.

我想替换存储在ArrayList中的重复数字(如果有的话)。我认为随机变量的数字。这是班级。

import java.util.*;

public class RandomNumbers {
// instance variables
private ArrayList<Integer> randomNumberList = new ArrayList<Integer>(); 
private Random randomNums = new Random();

public RandomNumbers(){
    // generating and adding random numbers to the list
    for (int i=0; i<MemoryGame.totalAnswers; i++)
        randomNumberList.add(randomNums.nextInt(32));

    System.out.println("Numbers in the list: " + randomNumberList);
    System.out.println("");
}

public ArrayList<Integer> getRandomNumbers(){
    return randomNumberList;
}
}

My school book tells me how to add,remove and retrieve a number, but not how to replace one that is duplicated.

我的学校书告诉我如何添加,删除和检索数字,但不知道如何替换重复的数字。

thanks.

4 个解决方案

#1

If you are not limited to ArrayList, use a HashSet<Integer> instead (or better yet, a LinkedHashSet). HashSet<Integer> will garantee you not to have duplicated values in the collection, LinkedHashSet<Integer> will do the same and also preserve the ordering the the items.

如果您不限于ArrayList,请使用HashSet (或者更好的是LinkedHashSet)。 HashSet 将保证您不要在集合中具有重复值,LinkedHashSet 将执行相同操作并保留项目的排序。

If you insist on having an ArrayList, then do this :

如果你坚持使用ArrayList,那么执行以下操作:

public RandomNumbers(){
    HashSet<Integer> set = new HashSet<Integer>();

    // generating and adding random numbers to the list
    //for (int i=0; i<MemoryGame.totalAnswers; i++)
    while (set.size()<MemoryGame.totalAnswers)
        set.add(randomNums.nextInt(32));

    randomNumberList.addAll(set);  // dump the set in your ArrayList

    System.out.println("Numbers in the list: " + randomNumberList);
    System.out.println("");
}

Also, if MemoryGame.totalAnswers == 32, then you can speed up this process with a random list instead :

此外,如果MemoryGame.totalAnswers == 32,那么您可以使用随机列表加速此过程:

public RandomNumbers(){
    // generating and adding random numbers to the list
    for (int i=0; i<MemoryGame.totalAnswers; i++)
        randomNumberList.add(i);

    Collections.shuffle(randomNumberList);

    System.out.println("Numbers in the list: " + randomNumberList);
    System.out.println("");
}

** Update **

**更新**

Since MemoryGame.totalAnswers == 8, forget the last snippet. I'm leaving it there if anyone would happend to need it. You can skip the use of a Set entirely by folllowing pst's suggestion :

由于MemoryGame.totalAnswers == 8,请忘记最后一个片段。如果有人愿意,我会把它留在那里。您完全可以通过以下pst的建议跳过Set的使用:

public RandomNumbers(){
    // generating and adding random numbers to the list
    for (int i=0; i<32; i++)
        randomNumberList.add(i);

    Collections.shuffle(randomNumberList);

    // keep only the first ones we need
    randomNumberList.removeRange(MemoryGame.totalAnswers + 1, 32);

    System.out.println("Numbers in the list: " + randomNumberList);
    System.out.println("");
}

#2

For replacing an element in a position use the set() method:

要替换位置中的元素,请使用set()方法:

randomNumberList.set(index, element);

Of course, the logic to find out which elements are duplicated in the first place is up to you; if it doesn't make sense to have duplicate numbers for your problem, better use a Set data structure (for instance: HashSet, or LinkedHashSet if preserving insertion order when iterating is important for you) and keep adding random elements to the set until it has the desired size.

当然,找出哪些元素首先重复的逻辑取决于你;如果你的问题有重复数字是没有意义的,最好使用Set数据结构(例如:HashSet,或者在迭代时保留插入顺序对于你很重要的LinkedHashSet)并继续向集合中添加随机元素,直到它为止具有所需的大小。

#3

If the ultimate objective is a random list of distinct numbers, and the range of possible numbers is not much larger than the number of results required, consider a shuffle rather than replacing duplicates.

如果最终目标是不同数字的随机列表,并且可能数字的范围不比所需结果的数量大得多,则考虑改组而不是替换重复数。

#4

If all you want is as per your last comment

如果你想要的只是你最后的评论

8 random, non-repeated numbers from 0-31

从0到0的8个随机,非重复数字

You don't need any instance variables, random number generating code, or instance methods.
All you need is just this:

您不需要任何实例变量,随机数生成代码或实例方法。你只需要这样:

public static List<Integer> getRandomNumbers() {
    List<Integer> list = new ArrayList<Integer>();
    for (int i = 0; i < 32; i++)
        list.add(i);
    Collections.shuffle(list);
    return list.subList(0, 8);
}

#1