将元素从一个 ArrayList 移动到另一个

Question

我课程中的指导是：完成下面静态方法 transplantBlock 的定义，对于任何非负整数 n，从 ArrayList fromList 中从索引开始的元素开始删除一个包含 n 个元素的块，然后插入它们（按顺序）进入一个从索引目标开始的 ArrayList toList。（如果从索引start的元素到fromList的末尾少于n个元素，则该方法从索引start的元素到结尾移植整个"tail"的ArrayList。）

到目前为止我有这个：

public static void transplantBlock( ArrayList<String> fromList,
                                    ArrayList<String> toList,
                                    int start,
                                    int target,
                                    int n ) {
    for ( int i = 0; i < n; i++) {
        if ( fromList.size() > start) {
            fromList.remove(start);            
        }  
    }
}

public static void main( String[] args )
{
  String[] fromData = { "a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k" };
  ArrayList<String> fromList = new ArrayList<String>();
  for ( int i = 0; i < fromData.length; i++ )
    fromList.add( fromData[ i ] );

  String[] toData = { "z", "y", "x", "w", "v", "u", "t", "s" };
  ArrayList<String> toList = new ArrayList<String>();
  for ( int i = 0; i < toData.length; i++ )
    toList.add( toData[ i ] );

  transplantBlock( fromList, toList, 6, 3, 4 );

  System.out.println( "After:" );
  System.out.println( "   fromList: " + fromList );
  System.out.println( "   toList: " + toList );
}

输出应该是这样的：

After:
   fromList: [a, b, c, d, e, f, k]
   toList: [z, y, x, g, h, i, j, w, v, u, t, s]

我能够从 fromList 中删除正确的元素，但我不知道如何将它们添加到 toList。如果有人能帮我弄清楚我错过了什么，我将不胜感激。谢谢！

（旁注：这是填空作业，因此这不是 class 问题）

Answer 1

跟踪要在何处插入您刚删除的元素的索引：

int insertIndex = target;
for (int i = 0; i < n; i++) {
    if (fromList.size() > start) {
        String removed = fromList.remove(start);
        toList.add(insertIndex, removed);
        insertIndex++;
    }
}

Answer 2

List

中有一个add(int index, E element)方法

它应该看起来像：

ArrayList<String> myList = new ArrayList(Arrays.asList("a","b","c","d"));

myList.add(2, "x");

// List should look like [a, b, x, c, d] now

剩下的应该是微不足道的。

Answer 3

public static void transplantBlock( ArrayList<String> fromList,
                                    ArrayList<String> toList,
                                    int start,
                                    int target,
                                    int n )


   {
    for (int i = 0; i < n; i++)
     {
        if (fromList.size() > start)
         {
            String removed = fromList.remove(start);
            toList.add(target, removed);
            target++;
        }
    }
   }


 public static void main( String[] args )
{
  String[] fromData = { "a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k" };
  ArrayList<String> fromList = new ArrayList<String>();
  for ( int i = 0; i < fromData.length; i++ )
    fromList.add( fromData[ i ] );

  String[] toData = { "z", "y", "x", "w", "v", "u", "t", "s" };
  ArrayList<String> toList = new ArrayList<String>();
  for ( int i = 0; i < toData.length; i++ )
    toList.add( toData[ i ] );

  transplantBlock( fromList, toList, 6, 3, 4 );

  System.out.println( "After:" );
  System.out.println( "   fromList: " + fromList );
  System.out.println( "   toList: " + toList );
}

将元素从一个 ArrayList 移动到另一个

Moving elements from one ArrayList to another

java

arraylist