C#节点指针问题

时间:2015-08-29 06:25:11

标签: c# tree

我在使用C#设置子节点时遇到了一些问题。我正在尝试构建一个节点树,其中每个节点都包含一个int值,并且最多可以有一些等于它的值的子节点。

当我在一个寻找空(空)子节点的节点中进行迭代时,我的问题出现了,这样我就可以在该位置添加一个新节点。我可以找到并返回null节点,但是当我将新节点设置为它时,它会失去与父节点的连接。

因此,如果我添加1个节点,那么它会链接到我的头节点,但是如果我尝试添加第二个节点,它就不会成为头节点的子节点。我试图通过单元测试来构建它,所以这里是测试代码,显示头部确实没有显示新节点作为它的孩子(也通过visual studio调试器确认):

  [TestMethod]
  public void addSecondNodeAsFirstChildToHead()
  {
     //arange
     Problem3 p3 = new Problem3();
     p3.addNode(2, p3._head);
     Node expected = null;
     Node expected2 = p3._head.children[0];
     int count = 2;

     //act
     Node actual = p3.addNode(1, p3._head);
     Node expected3 = p3._head.children[0];

     //assert
     Assert.AreNotEqual(expected, actual, "Node not added"); //pass
     Assert.AreNotEqual(expected2, actual, "Node not added as first child"); //pass
     Assert.AreEqual(expected3, actual, "Node not added as first child"); //FAILS HERE
     Assert.AreEqual(count, p3.nodeCount, "Not added"); //pass
  }

这是我的代码。

public class Node
   {
      public Node[] children;
      public int data;

      public Node(int value)
      {
         data = value;
         children = new Node[value];

         for(int i = 0; i < value; i++)
         {
            children[i] = null;
         }
      }
   }

   public class Problem3
   {
      public Node _head;
      public int nodeCount;

      public Problem3()
      {
         _head = null;
         nodeCount = 0;
      }

      public Node addNode(int value, Node currentNode)
      {
         if(value < 1)
         {
            return null;
         }

         Node temp = new Node(value);

         //check head
         if (_head == null)
         {
            _head = temp;
            nodeCount++;
            return _head;
         }

         //start at Current Node
         if (currentNode == null)
         {
            currentNode = temp;
            nodeCount++;
            return currentNode;
         }

         //find first empty child
         Node emptyChild = findEmptyChild(currentNode);
         emptyChild = temp;
         nodeCount++;
         return emptyChild;
      }

      public Node findEmptyChild(Node currentNode)
      {
         Node emptyChild = null;
         //find first empty child of current node
         for (int i = 0; i < currentNode.children.Length; i++)
         {
            if (currentNode.children[i] == null)
            {
               return currentNode.children[i];
            }
         }
         //move to first child and check it's children for an empty
         //**this causes values to always accumulate on left side of the tree
         emptyChild = findEmptyChild(currentNode.children[0]);
         return emptyChild;
      }

我觉得问题是我试图将节点视为指针,就像在C ++中一样,但是它没有像我期望的那样工作。

2 个答案:

答案 0 :(得分:2)

函数不可能将句柄(或指针)返回到尚不存在的东西。要么初始化函数内部不存在的值,要么提供足够的变量使其在函数外部初始化。

一种解决方案是将函数findEmptyChild重命名为initializeEmptyChild(Node currentNode, Node newNode),向其添加一个Node参数(当调用它为temp值时) ,并在return之前的循环中初始化以前为空的NodecurrentNode.children[i] = newNode

另一个解决方案不是只返回一个Node而是返回两个值,一个父节点和一个找到空子项的索引Tuple<Node, int> findEmptyChild(Node currentNode),而不是返回return currentNode.children[i]你做return new Tuple<Node, int>(currentNode, i)。调用该函数时,您将代码更改为

var parentAndIndex = findEmptyChild(currentNode);
parentAndIndex.Item1.children[parentAndIndex.Item2] = temp;

答案 1 :(得分:1)

查看代码的这一部分:

Node temp = new Node(value);
//...
Node emptyChild = findEmptyChild(currentNode);
emptyChild = temp;

您正在将emptyChild分配给新节点,这样做会“松散”与任何父节点的连接。你应该写这样的东西:

emptyChild.data = temp.data;
emptyChild.children = temp.children;

正如其他人所说,使用空检查的方法可以改进。您提到Node.data包含给定节点的子节点数,因此您可以简单地说,当您有Node.data == 0时,该节点应被视为空或空。例如,而不是:

rootNode.children[0] = null; // rootNode can have a lot of children
rootNode.children[1] = null;
//...
你会得到:

rootNode.children[0] = new Node(0);
rootNode.children[1] = new Node(0);
//...

此时您的代码看起来与此类似:

public class Node
{
    public Node[] children;
    public int data;

    public Node(int value)
    {
        data = value;
        children = new Node[value];

        // Instead of "pointing" to null,
        // create a new empty node for each child.
        for (int i = 0; i < value; i++)
        {
            children[i] = new Node(0);
        }
    }
}

public class Problem3
{
    public Node _head;
    public int nodeCount;

    public Problem3()
    {
        _head = null;
        nodeCount = 0;
    }

    public Node addNode(int value, Node currentNode)
    {
        if (value < 1)
        {
            return null;
        }

        Node temp = new Node(value);

        //check head
        if (_head == null)
        {
            _head = temp;
            nodeCount++;
            return _head;
        }

        //start at Current Node
        if (currentNode == null)
        {
            currentNode = temp;
            nodeCount++;
            return currentNode;
        }

        //find first empty child
        Node emptyChild = findEmptyChild(currentNode);
        if (emptyChild != null)
        {
            emptyChild.data = temp.data;
            emptyChild.children = temp.children;
            nodeCount++;
        }
        return emptyChild;
    }

    public Node findEmptyChild(Node currentNode)
    {
        // Null checking.
        if (currentNode == null)
            return null;

        // If current node is empty, return it.
        if (currentNode.data == 0)
            return currentNode;

        // If current node is non-empty, check its children.
        // If no child is empty, null will be returned.
        // You could change this method to check even the
        // children of the children and so on...
        return currentNode.children.FirstOrDefault(node => node.data == 0);
    }
}

现在让我们看看测试部分(请参阅评论以获得澄清):

[TestMethod]
public void addSecondNodeAsFirstChildToHead()
{
    //arange
    Problem3 p3 = new Problem3();
    p3.addNode(2, p3._head); // Adding two empty nodes to _head, this means that now _head can
                             // contain two nodes, but for now they are empty (think of them as
                             // being "null", even if it's not true)
    Node expected = null;
    Node expected2 = p3._head.children[0]; // Should be the first of the empty nodes added before.
                                           // Be careful: if you later change p3._head.children[0]
                                           // values, expected2 will change too, because they are
                                           // now pointing to the same object in memory
    int count = 2;

    //act
    Node actual = p3.addNode(1, p3._head); // Now we add a non-empty node to _head, this means
                                           // that we will have a total of two non-empty nodes:
                                           // this one fresly added and _head (added before)
    Node expected3 = p3._head.children[0]; // This was an empty node, but now should be non-empty
                                           // because of the statement above. Now expected2 should
                                           // be non-empty too.

    //assert
    Assert.AreNotEqual(expected, actual, "Node not added"); //pass

    // This assert won't work anymore, because expected2, expected 3 and actual 
    // are now pointing at the same object in memory: p3._head.children[0].
    // In your code, this assert was working because 
    // In order to make it work, you should replace this statement:
    //    Node expected2 = p3._head.children[0];
    // with this one:
    //    Node expected2 = new Node(0); // Create an empty node.
    //    expected2.data = p3._head.children[0].data; // Copy data
    //    expected2.children = p3._head.children[0].children;
    // This will make a copy of the node instead of changing its reference.
    Assert.AreNotEqual(expected2, actual, "Node not added as first child");

    // Now this will work.
    Assert.AreEqual(expected3, actual, "Node not added as first child");
    Assert.AreEqual(count, p3.nodeCount, "Not added"); //pass
}