唯一随机生成的整数的Java数组

问题描述

public static int[] uniqueRandomElements (int size) {

    int[] a = new int[size];

    for (int i = 0; i < size; i++) {
        a[i] = (int)(Math.random()*10);

        for (int j = 0; j < i; j++) {
            if (a[i] == a[j]) {
                a[j] = (int)(Math.random()*10);
            }
        }
    }

    for (int i = 0; i < a.length; i++) {
        System.out.print(a[i]+" ");
    }
    System.out.println();
    return a;
}

我上面有一个方法，它应该生成用户指定的随机元素数组.随机生成的整数应该介于 0 和 10 之间.我能够生成随机整数，但我遇到的问题是检查唯一性.我在上面的代码中尝试检查唯一性，但数组仍然包含整数的重复项.我做错了什么，有人可以给我一个提示吗?

I have a method above which should generate an array of random elements that the user specifies. The randomly generated integers should be between 0 and 10 inclusive. I am able to generate random integers but the problem I have is checking for uniqueness. My attempt to check for uniqueness is in my code above but the array still contains duplicates of integers. What am I doing wrong and could someone give me a hint?

推荐答案

for (int i = 0; i < size; i++) {
    a[i] = (int)(Math.random()*10);

    for (int j = 0; j < i; j++) {
        if (a[i] == a[j]) {
            a[j] = (int)(Math.random()*10); //What's this! Another random number!
        }
    }
}

您确实找到了重复值.但是，您将其替换为另一个可能重复的随机数.相反，试试这个:

You do find the duplicate values. However, you replace it with another random number that may be a duplicate. Instead, try this:

for (int i = 0; i < size; i++) {
    a[i] = (int)(Math.random()*10);//note, this generates numbers from [0,9]

    for (int j = 0; j < i; j++) {
        if (a[i] == a[j]) {
            i--; //if a[i] is a duplicate of a[j], then run the outer loop on i again
            break;
        }
    }
}

然而，这种方法效率低下.我建议制作一个数字列表，然后将其随机化:

However, this method is inefficient. I recommend making a list of numbers, then randomizing it:

ArrayList<Integer> a = new ArrayList<>(11);
for (int i = 0; i <= 10; i++){ //to generate from 0-10 inclusive.
                               //For 0-9 inclusive, remove the = on the <=
    a.add(i);
}
Collections.shuffle(a);
a = a.sublist(0,4);
//turn into array

或者你可以这样做:

ArrayList<Integer> list = new ArrayList<>(11);
for (int i = 0; i <= 10; i++){
    list.add(i);
}
int[] a = new int[size];
for (int count = 0; count < size; count++){
    a[count] = list.remove((int)(Math.random() * list.size()));
}

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