Java面试--二叉树

面试题:讲一下二叉树的遍历

一、二叉树遍历方式
1、前序遍历：按照“根左右”,先遍历根节点，再遍历左子树 ，再遍历右子树

2、中序遍历：按照“左根右“,先遍历左子树，再遍历根节点，最后遍历右子树

3、后续遍历：按照“左右根”，先遍历左子树，再遍历右子树，最后遍历根节点

二、二叉树的java实现
定义节点类：

public class Node {
    public long data;
    public String sData;
    public Node leftChild;
    public Node rightChild;

    public Node(long value,String sData){
        this.data = value;
        this.sData = sData;
    }
}

定义树：

public class Tree {
    public Node root;
    public void insert(long value,String sData){
        Node newNode = new Node(value,sData);   //封装节点
        Node current = root;  //引用当前节点
        Node parent;          //引用父节点
        //如果root为null , 也就是第一次插入的时候
        if( root == null ){
            root = newNode;
            return;
        }
        else{
            while(true) {
                parent = current;
                if (current.data > value) {
                    current = current.leftChild;
                    if( current == null ) {
                        parent.leftChild = newNode;
                        return;
                    }
                } else {
                    current = current.rightChild;
                    if( current == null ){
                        parent.rightChild = newNode;
                        return;
                    }
                }
            }
        }
    }
    //查找节点
    public Node find(long value){
        Node current = root;
        while(current.data != value){
            if( current.data > value ){
                current = current.leftChild;
            }
            else{
                current = current.rightChild;
            }
            if(current == null){
                return null;
            }
        }
        return current;
    }
    //删除节点
}

三、二叉树遍历的java实现
1、前序遍历：

public static void preOrder(BinNode node) {
    public void preOrder(Node localLoad) {
        if( localLoad != null ){
            System.out.println(localLoad.data + "," + localLoad.sData);
            preOrder(localLoad.leftChild);
            preOrder(localLoad.rightChild);
        }
    }
}

测试：

public class TestTree {
    public static void main(String[] args) {
        Tree tree = new Tree();
        tree.insert(10,"James");
        tree.insert(20,"Tom");
        tree.insert(15,"Marry");
        tree.insert(3,"Kobe");
        tree.insert(4,"Naruto");
        tree.insert(90,"LiSi");
        tree.preOrder(tree.root);
    }
}
//插入之后的状态：
      10
 3          20
   4     15     90
//输出结果：
10,James
3,Kobe
4,Naruto
20,Tom
15,Marry
90,LiSi

2、中序遍历：

public void inOrder(Node localNode) {
    if( localNode != null ) {
        inOrder(localNode.leftChild);
        System.out.println(localNode.data + "," + localNode.sData);
        inOrder(localNode.rightChild);
    }
}

测试：

public class TestTree {
    public static void main(String[] args) {
        Tree tree = new Tree();
        tree.insert(10,"James");
        tree.insert(20,"Tom");
        tree.insert(15,"Marry");
        tree.insert(3,"Kobe");
        tree.insert(4,"Naruto");
        tree.insert(90,"LiSi");
        tree.inOrder(tree.root);
    }
}
//插入之后的状态：
      10
 3          20
   4     15     90
//输出结果：
3,Kobe
4,Naruto
10,James
15,Marry
20,Tom
90,LiSi

3、后序遍历：

public void postOrder(Node localNode) {
   if( localNode != null ) {
        postOrder(localNode.leftChild);
        postOrder(localNode.rightChild);
        System.out.println(localNode.data + "," + localNode.sData);
    }
}

测试：

public class TestTree {
    public static void main(String[] args) {
        Tree tree = new Tree();
        tree.insert(10,"James");
        tree.insert(20,"Tom");
        tree.insert(15,"Marry");
        tree.insert(3,"Kobe");
        tree.insert(4,"Naruto");
        tree.insert(90,"LiSi");
        postOrder(tree.root);
    }
}
//插入之后的状态：
      10
 3          20
   4     15     90
//输出结果：
4,Naruto
3,Kobe
15,Marry
90,LiSi
20,Tom
10,James

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Java面试的完整博客目录如下：Java笔试面试目录

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