我在我的AVL树实现中遇到了一些问题。所有旋转和添加的代码似乎都是正确的，我运行该程序以彻底检查它是否在逻辑上正确运行。我似乎在我的树遍历（按顺序）中遇到问题，因为它只输出假定的100的几个整数。此外，无论我输入什么，搜索总是失败。我似乎无法掌握正在发生的事情，但我怀疑它与一些空指针有关。下面是AVL树的代码，我想知道AddNode方法或旋转方法中是否有任何不正确的代码，但它们看起来很好..这些类是Node类，AVL类和AVL树类，它是主类
节点类
private int data;
private Node left;
private Node right;
private int height;
public Node(int m) {
data = m;
left = null;
right = null;
height = 0;
}
public void setToleft(Node newleft) {
left = newleft;
}
public Node getleftNode() {
return left;
}
public void setToright(Node newright) {
right = newright;
}
public Node getrightNode() {
return right;
}
public int getData() {
return data;
}
public int getHeight(){
return height;
}
public void setHeight(int height){
this.height = height;
}
AVL课程
public Node root;
public AVL(int root) {
this.root = new Node(root); // since root presently has no left or right children, height is currently 0
}
public int Height(Node n) {
if (n == null) { //basis step
return -1;
} else { //add one for every path
if (n.getleftNode() == null && n.getrightNode() == null) {
return 0;
}
return 1 + Math.max(Height(n.getleftNode()), Height(n.getrightNode()));
}
}
public void add(int data) {
addNode(data, root);
root.setHeight(Math.max(Height(root.getleftNode()), Height(root.getrightNode())) + 1);
}
public void addNode(int data, Node n) {
if (data < n.getData()) {
if (n.getleftNode() == null) {
n.setToleft(new Node(data));
} else {
addNode(data, n.getleftNode());
}
n.setHeight(Math.max(Height(n.getleftNode()), Height(n.getrightNode())) + 1);
if ((Height(n.getleftNode()) + 1) - (Height(n.getrightNode()) + 1) == Math.abs(2)) {
if (data < n.getleftNode().getData()) {
n = LLRotation(n);
} else {
n = LRRotation(n);
}
}
} else if (data >= n.getData()) { //>= also caters for duplicates and inserts them infront of same value
if (n.getrightNode() == null) {
n.setToright(new Node(data));
} else {
addNode(data, n.getrightNode());
}
n.setHeight(Math.max(Height(n.getleftNode()), Height(n.getrightNode())) + 1);
if ((Height(n.getrightNode()) + 1) - (Height(n.getleftNode()) + 1) == Math.abs(2)) {
if (data >= n.getrightNode().getData()) {
n = RRRotation(n);
} else {
n = RLRotation(n);
}
}
}
}
public Node LLRotation(Node n) { //single
Node n1 = n.getleftNode();
n.setToleft(n1.getrightNode());
n1.setToright(n);
n.setHeight(Math.max(Height(n.getleftNode()), Height(n.getrightNode())) + 1);
n1.setHeight(Math.max(Height(n1.getleftNode()), Height(n)) + 1);
//compares heights of left and right subtrees and gets max
//the above source code is of course vital since the node height must be resetted after rotations
//adding 1 at the end of the last two code lines is important since
//initially the height is only calculated from subtrees onwards
//same for single right rotation below
return n1;
}
public Node RRRotation(Node n) { //single
Node n1 = n.getrightNode();
n.setToright(n1.getleftNode());
n1.setToleft(n);
n.setHeight(Math.max(Height(n.getleftNode()), Height(n.getrightNode())) + 1);
n1.setHeight(Math.max(Height(n1.getrightNode()), Height(n)) + 1);
return n1;
}
public Node LRRotation(Node n) { //double
n.setToleft(RRRotation(n.getleftNode()));
return LLRotation(n);
}
public Node RLRotation(Node n) { //double
n.setToright(LLRotation(n.getrightNode()));
return RRRotation(n);
}
public void inOrderTraversal(Node n) {
if (n != null) {
inOrderTraversal(n.getleftNode()); //recursive call to the left subtree
System.out.println(n.getData()); //line which makes the actual node to display its data
inOrderTraversal(n.getrightNode()); //recursive call to the right subtree
}
}
public void traverse() {
inOrderTraversal(root); // can be called in main class to automatically traverse tree from its root
}
public int search(int x) {
try {
if (x == root.getData()) { //basis step
System.out.println("Item found!");
return x;
}
if (x < root.getData()) {
root = root.getleftNode();
return search(x);//recursive call
} else {
root = root.getrightNode();
return search(x);//recursive call
}
} catch (NullPointerException e) {
System.out.println ("Search failed!");
return 0;
}
}
主类
public static void main(String[] args) throws IOException {
Scanner s = new Scanner(System.in);
AVL tree = null;
int choice = 0;
System.out.println("AVL TREE");
System.out.println("\n Choose an option from the menu: ");
System.out.println("\n\t 1.) Create file of 100 integers");
System.out.println("\n\t 2.) Create the tree");
System.out.println("\n\t 3.) In-Order traverse and show tree");
System.out.println("\n\t 4.) Search for integer");
System.out.println("\n\t 5.) Quit");
while (choice != 5) {
System.out.print("\nChoice: ");
choice = s.nextInt();
switch (choice) {
case 1:
createFile();
break;
case 2:
try {
FileReader readto = new FileReader("Integers.txt");
BufferedReader br = new BufferedReader(readto);
String line = br.readLine(); //reads text at start of file
line = br.readLine(); // skipping empty lines
line = br.readLine();
line = br.readLine();
int root = Integer.parseInt(line); //extracts first integer from the line
System.out.println("Root: " + root);
tree = new AVL(root);
int x = 0;
while (x != 99) {
try {
line = br.readLine();
int next = Integer.parseInt(line);
tree.add(next);
System.out.println(next);
x++;
} catch (NumberFormatException e) {
};
}
System.out.println("Tree successfully populated!");
} catch (FileNotFoundException e) {
System.out.println("ERROR: File not found!");
}
break;
case 3:
System.out.println("In-Order traversel executed. The now balanced tree shall now be printed in");
System.out.println("ascending order and also the left and right children of each node shall be printed.\n");
System.out.println("Traversal: ");
tree.traverse();
break;
case 4:
System.out.print("Please enter the integer to be searched: ");
int x = s.nextInt();
System.out.println(tree.search(x));
break;
case 5:
System.exit(0);
break;
default:
System.out.println("ERROR: Choice out of bounds!");
}
}
}
static void createFile() throws IOException {
Random r = new Random();
File intfile = new File("Integers.txt");
FileWriter writeto = new FileWriter("Integers.txt");
BufferedWriter bw = new BufferedWriter(writeto);
if (!(intfile.exists())) {
System.out.println("ERROR: File not found!");
} else {
bw.write("The following integers are randomly generated");
bw.newLine();
bw.write("and will be used to construct the AVL tree:");
bw.newLine();
bw.newLine();
int x;
System.out.println("The following random numbers shall be used to build the AVL tree: \n");
for (int i = 0; i < 100; i++) {
x = r.nextInt(100) + 1;
bw.write(String.valueOf(x));
bw.newLine();
System.out.println(x);
}
bw.close();
}
}
遍历的输出如下：
穿越： 44 53 54 54 77
假设输入了100个整数，其中包括这些整数。但遍历的输出只是这个。
搜索输出如下： 选择：4 请输入要搜索的整数：44 找到物品！ 44
选择：4 请输入要搜索的整数：100 搜索失败！ 0
100和44都是添加到树中的整数，但是找到了44个而不是100个..我不明白..
任何人都可以指导我找到解决方案..？
提前致谢：）
答案 0 :(得分：1)
嗯，首先显而易见的事情......在search方法中，您滥用root变量，该变量保存树的根，并在搜索过程中将其设置为新值。因此，在第一次搜索之后，root指向搜索中遍历的最后一个节点，而不再指向树的根节点。从那时起，所有后续搜索都不可能找到任何内容。
由于您的搜索是递归的，请尝试将要搜索的节点作为参数传递：
int search(Node node, int key) {
if (node == null) {
return 0; // missing from tree
} else if (key < node.getData()) {
return search(node.getLeft(), key);
} else if (key > node.getData()) {
return search(node.getRight(), key);
} else {
return node.getData(); // found it
}
}
（已编辑以解决评论）您可能需要公开此方法，就像使用公开的包装器对add / addNode方法对一样，内部实施：
public int search(int key) {
return searchNode(root, key);
}
private int searchNode(Node node, int key) {
// Perform the recursive search, as above
}
还有与add / addNode方法相关的其他问题。也许我只是忽略了它，但是如果旋转使得必要的话，你无处调整树的根节点。实际上，这会导致您的树失去平衡，随着时间的推移会失去AVL属性。