PTA二叉树的遍历java

以下是PTA二叉树的遍历的Java代码示例：

import java.util.Scanner;

class TreeNode {
    int val;
    TreeNode left;
    TreeNode right;

    TreeNode(int val) {
        this.val = val;
        this.left = null;
        this.right = null;
    }
}

public class BinaryTreeTraversal {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        TreeNode[] nodes = new TreeNode[n];
        for (int i = 0; i < n; i++) {
            nodes[i] = new TreeNode(sc.nextInt());
        }
        for (int i = 0; i < n; i++) {
            int leftIndex = sc.nextInt();
            int rightIndex = sc.nextInt();
            if (leftIndex != -1) {
                nodes[i].left = nodes[leftIndex];
            }
            if (rightIndex != -1) {
                nodes[i].right = nodes[rightIndex];
            }
        }
        sc.close();

        System.out.print("Preorder traversal: ");
        preorderTraversal(nodes[0]);
        System.out.println();

        System.out.print("Inorder traversal: ");
        inorderTraversal(nodes[0]);
        System.out.println();

        System.out.print("Postorder traversal: ");
        postorderTraversal(nodes[0]);
        System.out.println();
    }

    public static void preorderTraversal(TreeNode root) {
        if (root == null) {
            return;
        }
        System.out.print(root.val + " ");
        preorderTraversal(root.left);
        preorderTraversal(root.right);
    }

    public static void inorderTraversal(TreeNode root) {
        if (root == null) {
            return;
        }
        inorderTraversal(root.left);
        System.out.print(root.val + " ");
        inorderTraversal(root.right);
    }

    public static void postorderTraversal(TreeNode root) {
        if (root == null) {
            return;
        }
        postorderTraversal(root.left);
        postorderTraversal(root.right);
        System.out.print(root.val + " ");
    }
}