我在添加值时遇到问题，这些值会在我的 234 树中创建超出第一级的新级别。我的方法在根对象上创建子对象，但无法为任何其他节点创建子对象。我能够创建和插入给定数量的数据对象，只要它们不填充导致它创建子节点的节点......我已经认真梳理了好几天。
我的问题基本上是基于我的代码。我的方法（特别是插入方法）是否允许在根目录下创建子节点？
树类
public class Tree234 {
public Node root = new Node(); // make root node
public int find(String key) {
Node focus = root;
int childNumber;
while (true) {
if ((childNumber = focus.findItem(key)) != -1) {
return childNumber; // found it
} else if (focus.isLeaf()) {
return -1; // can't find it
} else // search deeper
{
focus = getNextChild(focus, key);
}
} // end while
}
// insert a DataItem
public void insert(String dWord) { // Performs the splits
// in a top-down (root -----> leaf) fashion.
Node focus = root;
DataItem tempItem = new DataItem(dWord);
while (true) {
if (focus.isFull()) { // if node full
System.out.println("Need to split!");
split(focus); // split it
System.out.println("Splint done?");
focus = focus.getParent(); // back up
// search once
focus = getNextChild(focus, dWord);
} // end if (node is full)
else if (focus.isLeaf()) { // if node is leaf
break; // jump to insert
} else { // node is not full, not a leaf; so go to lower level
focus = getNextChild(focus, dWord);
}
} // end while
// insert new DataItem
focus.insertItem(tempItem);
} // end insert
public void split(Node thisNode) { // split the node
// assumes node is full
DataItem itemB, itemC;
Node parent, child2, child3;
int itemIndex;
// two right most items are removed from the node and stored
itemC = thisNode.removeItem(); // remove items from
itemB = thisNode.removeItem(); // this node
child2 = thisNode.disconnectChild(2); // remove children
child3 = thisNode.disconnectChild(3); // from this node
// make new node, goes to the right of the node being split
Node newRight = new Node();
if (thisNode == root) { // if this is the root
// make new root
root = new Node();
// root is our parent
parent = root;
// connect to parent
root.connectChild(0, thisNode);
} else {// this node not the root get parent
parent = thisNode.getParent();
}
// deal with parent
// item B is inserted in the parent node
itemIndex = parent.insertItem(itemB); // deal with parent
// total items?
int n = parent.getNumItems();
// move parent's connections
// one child to the right
for (int j = n - 1; j < itemIndex; j--) {
Node temp = parent.disconnectChild(j);
parent.connectChild(j + 1, temp);
}
// connect newRight to parent
parent.connectChild(itemIndex + 1, newRight);
// deal with newRight
newRight.insertItem(itemC); // item C to newRight
newRight.connectChild(0, child2); // connect to 0 and 1
newRight.connectChild(1, child3); // on newRight
} // end split()
public Node getNextChild(Node theNode, String keyWord) {
int j;
// assumes node is not empty, not full, not a leaf
int numItems = theNode.getNumItems();
// for each item in node
for (j = 0; j < numItems; j++) {
// is the value given less than the value at the
//first index of the array?
if (keyWord.compareToIgnoreCase(theNode.getItem(j).dData) < 0) {
// if so, return left child so we can use it at another
// point in time
return theNode.getChild(j);
}
} // end for
return theNode.getChild(j);
// otherwise, our value is greater we're greater, so
// we return right child (the child right after the
// value given, greater)
}
public void displayTree() {
recDisplayTree(root, 0, 0);
}
public void recDisplayTree(Node thisNode, int level, int childNumber) {
System.out.print("level=" + level + " child=" + childNumber + " ");
thisNode.displayNode(); // display this node
// call ourselves for each child of this node
int numItems = thisNode.getNumItems();
for (int j = 0; j < numItems + 1; j++) {
Node nextNode = thisNode.getChild(j);
if (nextNode != null) {
recDisplayTree(nextNode, level + 1, j);
} else {
return;
}
}
} // end recDisplayTree()
}
通常我只会发布我要查询的特定代码。但是，此特定方法也跳到其他两个类中。所以我认为看看我如何设置它们会有所帮助。
节点类
public class Node {
// Max size
private static final int SIZE = 4;
public int numItems;
public Node parent;
public Node children[] = new Node[SIZE];
public DataItem items[] = new DataItem[SIZE - 1];
public void connectChild(int childNum, Node child) { // Connect child to this Node
children[childNum] = child;
if (child != null) {
child.parent = this;
}
}
public Node disconnectChild(int childNum) { // Disconnect child from this Node
Node temp = children[childNum];
children[childNum] = null;
return temp;
}
public Node getChild(int childNum) { // Returns child
return children[childNum];
}
public Node getParent() { // Returns parent
return parent;
}
public Boolean isLeaf() {
// test if child is a leaf
return children[0] == null;
}
public int getNumItems() {
return numItems;
}
public DataItem getItem(int index) {
return items[index];
}
public Boolean isFull() {
return numItems == SIZE - 1;
}
public int findItem(String term) {
for (int j = 0; j < SIZE; j++) {
if (items[j] == null) {
break;
} else if (items[j].dData.equalsIgnoreCase(term)) {
return j;
}
}
return -1;
} // end findItem()
public int insertItem(DataItem newItem) {
if (findItem(newItem.dData) != -1) {
items[findItem(newItem.dData)].count++;
return 0;
}
numItems++; // will add new item
String newKey = newItem.dData;
for (int j = numItems-1; j >= 0; j--) {
if (items[j] != null){
System.out.println(items[j].dData);
}
if (items[j] == null) {
continue;
} else {
String itsKey = items[j].dData;
if (newKey.compareToIgnoreCase(itsKey) < 0) {
items[j + 1] = items[j];
} else {
items[j + 1] = newItem;
return j + 1;
}
} // end else (not null)
} // end for ----> // shifted all items,
items[0] = newItem; // insert new item
return 0;
} // end insertItem()
public DataItem removeItem() {
DataItem temp = items[numItems - 1];
items[numItems - 1] = null;
numItems--;
return temp;
}
public void displayNode() {
for (int j = 0; j < numItems; j++) {
items[j].displayItem();
}
System.out.println();
}
} // end class Node
我现在将所有内容都设置为公开，因为我只是在测试代码的结构。
数据项类
public class DataItem {
public String dData;
public int count;
public DataItem(String term) {
dData = term;
count = 1;
}
public String getItem() {
return this.dData;
}
public int getCount() {
return this.count;
}
public void displayItem() {
System.out.print("\nWord: " + dData + "\t\tCount: " + count);
}
}
这是我将 DataItem 对象添加到树的方法。
public class Main {
public static void main(String[] args) {
Tree234 tree = new Tree234();
for (int i = 0; i < 13; i++) {
String temp = RandomName.getLast();
System.out.println(temp);
tree.insert(temp);
}
tree.displayTree();
}
输出
Townsend
George
Townsend
Welch
Townsend
Clemons
George
Rose
George
Bond
Townsend
Clemons
Bowers
Clemons
Bond
Foreman
Townsend
George
Clemons
Hahn
Townsend
Alston
Bond
Petersen
Townsend
Hahn
Hansen
George
Hahn
Moses
Hansen
level=0 child=0
Word: George Count: 1
Word: Petersen Count: 1
level=1 child=0
Word: Bowers Count: 1
level=2 child=0
Word: Alston Count: 1
Word: Bond Count: 1
level=2 child=1
Word: Clemons Count: 1
Word: Foreman Count: 1
level=1 child=1
Word: Hahn Count: 1
Word: Hansen Count: 1
Word: Moses Count: 1
level=1 child=2
Word: Townsend Count: 1
树“似乎”可以工作，但是添加超过 10 个名称开始使其不稳定。它根本无法处理 15 个或更多。
输出 15 或更多
Bowman
Moore
Bowman
Anthony
Moore
Bowman
Graham
Moore
Nielsen
Exception in thread "main" java.lang.NullPointerException
Moore
Camacho
Bowman
Graham
Herman
Graham
Gallagher
Moore
Bowman
Camacho
Hartman
Herman
Daniels
Gallagher
Camacho
Snyder
at dataPackage.Tree234.insert(Tree234.java:40)
at testPackage.Main.main(Main.java:31)
X:\source\234Tree\234Tree\nbproject\build-impl.xml:1040: The following error occurred while executing this line:
X:\source\234Tree\234Tree\nbproject\build-impl.xml:805: Java returned: 1
BUILD FAILED (total time: 0 seconds)
我对算法还是很陌生，所以我可能完全错过了一些简单的东西。我开始认为插入方法很好，但我可能没有正确拆分。这就是为什么我现在可以插入到第 2 级而不是更远的原因。感谢您提供的任何见解。