根据前序和中序构建二叉树

题目：

根据二叉树的前序遍历和中序遍历构建二叉树，并进行层序遍历输出结果。

代码：

import java.util.*;

//节点
class Node {
    int val;
    Node left;
    Node right;

    Node(int val) {
        this.val = val;
    }
}

public class Main {

    // 递归构建树
    public static Node CreateTree(int[] front, int[] back) {
        int len = front.length;
        if (len == 0)
            return null;

        Node head = new Node(front[0]);

        // 寻找中序的根节点
        int index = 0;
        for (int i = 0; i < len; i++) {
            if (front[0] == back[i]) {
                index = i;
                break;
            }
        }
        // 拆分2个数组
        int[] frontLeft = Arrays.copyOfRange(front, 1, index + 1);
        int[] frontRight = Arrays.copyOfRange(front, index + 1, len);

        int[] backLeft = Arrays.copyOfRange(back, 0, index);
        int[] backRight = Arrays.copyOfRange(back, index + 1, len);

        head.left = CreateTree(frontLeft, backLeft);
        head.right = CreateTree(frontRight, backRight);

        return head;
    }

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        while (in.hasNextInt()) {

            int n = in.nextInt();
            int[] front = new int[n];
            int[] back = new int[n];
            for (int i = 0; i < n; i++)
                front[i] = in.nextInt();

            for (int i = 0; i < n; i++)
                back[i] = in.nextInt();

            Node head = CreateTree(front, back);

            // 层序遍历树
            //使用队列来存储
            Queue<Node> queue = new LinkedList<Node>();
            queue.add(head);

            int[] result = new int[n];
            int k = 0;
            while (queue.size() != 0) {
                Node visitedNode = queue.remove();
                result[k] = visitedNode.val;
                k++;

                if (visitedNode.left != null)
                    queue.add(visitedNode.left);

                if (visitedNode.right != null)
                    queue.add(visitedNode.right);
            }
            //输出结果
            for (int i = 0; i < n - 1; i++) {
                System.out.print(result[i] + " ");
            }
            System.out.print(result[n - 1]);
        }
    }

}