java - 检查两个 int 数组是否有重复元素，并从中提取重复元素之一

Question

我正在尝试编写一个方法 union()，它将返回一个 int 数组，它需要两个 int 数组参数并检查它们是否是集合，或者换句话说，它们之间是否存在重复。我写了另一种方法 isSet()，它接受一个数组参数并检查数组是否是一个集合。问题是我想检查 union 方法中的两个数组之间是否有重复项，如果有，我想提取其中一个重复项并将其放入 unionArray[] int 数组中。这是我到目前为止所尝试的。

public int[] union(int[] array1, int[] array2){
  
  int count = 0;
  if (isSet(array1) && isSet(array2)){
     for (int i = 0; i < array1.length; i++){
        for (int j = 0; j < array2.length; j++){
           if (array1[i] == array2[j]){ 
              System.out.println(array2[j]);
              count ++;
           }
        }
     }
  }
  int[] array3 = new int[array2.length - count];
     
  int[] unionArray = new int[array1.length + array3.length];
  int elementOfUnion = 0;
      
  for (int i = 0; i< array1.length; i++){
     unionArray[i] = array1[i];
     elementOfUnion = i + 1 ;
  }
  int index = 0;
  for (int i = elementOfUnion; i < unionArray.length; i++){
     unionArray[i] = array3[index];
     index++;
  }
  
  
  return unionArray;
}


public boolean isSet(int[] array){
  boolean duplicates = true;
  
  for (int i = 0; i < array.length; i++){
     for(int n = i+1; n < array.length; n++){
        if (array[i] == array[n])
           duplicates = false;
     }
  }
     
  return duplicates;
}

我试图做的是使用unionArray中的所有array1元素，检查array2是否与array1有任何重复，然后将所有不重复的元素从array2移动到新的array3，并将array3连接到unionArray。

标签： javaarraysunique

Answer 1

Collection使用API 或API会容易得多Stream。但是，您已经提到您想纯粹使用数组而不导入任何类来完成它，这将需要一些冗长（虽然简单）的处理单元。驱动逻辑的最重要理论是如何（如下所示）计算联合：

n(A U B) = n(A) + n(B) - n(A ∩ B)

和

n(Only A) = n(A) - n(A ∩ B)
n(Only B) = n(B) - n(A ∩ B)

下图描述了此解决方案的高级摘要：

其余的逻辑已经通过代码本身的注释非常清楚地提到了。

public class Main {
    public static void main(String[] args) {
        // Test
        display(union(new int[] { 1, 2, 3, 4 }, new int[] { 3, 4, 5, 6 }));
        display(union(new int[] { 1, 2, 3 }, new int[] { 4, 5, 6 }));
        display(union(new int[] { 1, 2, 3, 4 }, new int[] { 1, 2, 3, 4 }));
        display(union(new int[] { 1, 2, 3, 4 }, new int[] { 3, 4 }));
        display(union(new int[] { 1, 2, 3, 4 }, new int[] { 4, 5 }));
        display(union(new int[] { 1, 2, 3, 4, 5, 6 }, new int[] { 7, 8 }));
    }

    public static int[] union(int[] array1, int[] array2) {
        // Create an array of the length equal to that of the smaller of the two array
        // parameters
        int[] intersection = new int[array1.length <= array2.length ? array1.length : array2.length];
        int count = 0;

        // Put the duplicate elements into intersection[]
        for (int i = 0; i < array1.length; i++) {
            for (int j = 0; j < array2.length; j++) {
                if (array1[i] == array2[j]) {
                    intersection[count++] = array1[i];
                }
            }
        }

        // Create int []union of the length as per the n(A U B) = n(A) + n(B) - n(A ∩ B)
        int[] union = new int[array1.length + array2.length - count];

        // Copy array1[] minus intersection[] into union[]
        int lastIndex = copySourceOnly(array1, intersection, union, count, 0);

        // Copy array2[] minus intersection[] into union[]
        lastIndex = copySourceOnly(array2, intersection, union, count, lastIndex);

        // Copy intersection[] into union[]
        for (int i = 0; i < count; i++) {
            union[lastIndex + i] = intersection[i];
        }

        return union;
    }

    static int copySourceOnly(int[] source, int[] exclude, int[] target, int count, int startWith) {
        int j, lastIndex = startWith;
        for (int i = 0; i < source.length; i++) {
            // Check if source[i] is present in intersection[]
            for (j = 0; j < count; j++) {
                if (source[i] == exclude[j]) {
                    break;
                }
            }

            // If j has reached count, it means `break;` was not executed i.e. source[i] is
            // not present in intersection[]
            if (j == count) {
                target[lastIndex++] = source[i];

            }
        }
        return lastIndex;
    }

    static void display(int arr[]) {
        System.out.print("[");
        for (int i = 0; i < arr.length; i++) {
            System.out.print(i < arr.length - 1 ? arr[i] + ", " : arr[i]);
        }
        System.out.println("]");
    }
}

输出：

[1, 2, 5, 6, 3, 4]
[1, 2, 3, 4, 5, 6]
[1, 2, 3, 4]
[1, 2, 3, 4]
[1, 2, 3, 5, 4]
[1, 2, 3, 4, 5, 6, 7, 8]