Question

我无法理解，我的display()方法怎么办？我可以发誓我正确地将物品插入树中。

这是我的Node.java文件：

public class Node  {
    String data;
    Node left;
    Node right;

    public Node(Student s) {
        this.data = data;
        left = null;
        right = null;
    }
}

这是我的BinaryTree.java文件：

    public class BinaryTree {
    private Node root;

    public Node insert(Student s) {
        return insert(this.root, s);
    }

    private Node insert(Node n, Student s) {
        if(this.root == null) { // If the root is null.
            this.root = n;  // Then set root to node n.
            return n; // Return n which is null.
        }
        if(s.getLastName().compareTo(n.data) < 0) { // If the name that's passed in is less than 0.
            if(n.left == null) { // If the left node of the tree is empty.
                n.left = new Node(s); // Then create a left node.
                insert(n.left,s);
            }
            return n.left;
        } else if(s.getLastName().compareTo(n.data) > 0) { // If the name that's passed in is greater than 0.
            if(n.right == null) { // If the right node of the tree is empty.
                n.right = new Node(s); // Then create a right node.
                insert(n.right,s);          
            }
            return n.right;
        }
        return n; 
    }   

    public void display() {
        display(root);
    }

    private void display(Node root)  { 
        if(root == null) { 
            System.out.println("Nothing found.");
            System.exit(0);
        } else {
            display(root.right);
            System.out.println(root.data);
            display(root.left);
        }
    }
}

这是我的Student.java文件：

    public class Student {
    private String firstName;
    private String lastName;
    private String id;

    public Student(String first, String last, String Identification) {
        firstName = first;
        lastName = last;
        id = Identification;
    }

    public String getFirstName() {
        return firstName;
    }

    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }

    public String getLastName() {
        return lastName;
    }

    public void setLastName(String lastName) {
        this.lastName = lastName;
    }

    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }

    public boolean equals(String studentId) {
        return id.equals(studentId);    
    }

    public int compareTo(String s) {
        int lengthOfLongestString = 0; 
        int i = 0; 
        int a = 0;  
        int b = 0;

        if(lastName.length() < s.length()) { 
            lengthOfLongestString = lastName.length();      
        } else {
            lengthOfLongestString = s.length();  
        }

        if(lastName.charAt(0) == s.charAt(0)) {
            for(i = 0; i < lengthOfLongestString; i++) {
                if(lastName.charAt(i) != s.charAt(i)) {
                    a++;
                    b++;
                    break;
                }
            }       

            if(i == lengthOfLongestString - 1) { 
                return 0;
            }

            if(lastName.charAt(a) < s.charAt(b)) {
                return -1;
            }   
        }
        return 1;
        }
}

这是我的Main.java文件：

    public class Main {
    public static void main(String[] args) {
        Student student = new Student("hi", "bye", "brown");
        Student student2 = new Student("hi", "green", "now");

        BinaryTree bt = new BinaryTree();
        System.out.println(bt.insert(student));
        System.out.println(bt.insert(student2));
        bt.display();
    }
}

这是我的output：

null
null
Nothing found.

Answer 1

我猜你的插入不适用于root元素和实际插入后的额外插入调用。可能有以下变化可能有所帮助。

 ...
private Node insert(Node n, Student s) {
    if(this.root == null) { // If the root is null.
        this.root = new Node(s);  // Create a new node and return it
        return this.root; // Return n which is null.
    }
    if(s.getLastName().compareTo(n.data) < 0) { // If the name that's passed in is less than 0.
        if(n.left == null) { // If the left node of the tree is empty.
            n.left = new Node(s); // Then create a left node.
            //insert(n.left,s); // Guess this is not needed as the insert already happened
        }
        return n.left;
    } else if(s.getLastName().compareTo(n.data) > 0) { // If the name that's passed in is greater than 0.
        if(n.right == null) { // If the right node of the tree is empty.
            n.right = new Node(s); // Then create a right node.
            //insert(n.right,s); // Guess this is not needed as the insert already happened          
        }
        return n.right;
    }
  ...

希望它有所帮助！

为什么赢得我的二叉树显示？

1 个答案: