HDU1710—二叉树遍历 java编程

以下是HDU1710—二叉树遍历的Java代码实现，其中包括了前序遍历、中序遍历和后序遍历三种方法：

class TreeNode {
    int val;
    TreeNode left;
    TreeNode right;
    TreeNode(int x) { val = x; }
}

public class BinaryTreeTraversal {
    // 前序遍历
    public static void preOrderTraversal(TreeNode node) {
        if (node == null) {
            return;
        }
        System.out.print(node.val + " ");
        preOrderTraversal(node.left);
        preOrderTraversal(node.right);
    }

    // 中序遍历
    public static void inOrderTraversal(TreeNode node) {
        if (node == null) {
            return;
        }
        inOrderTraversal(node.left);
        System.out.print(node.val + " ");
        inOrderTraversal(node.right);
    }

    // 后序遍历
    public static void postOrderTraversal(TreeNode node) {
        if (node == null) {
            return;
        }
        postOrderTraversal(node.left);
        postOrderTraversal(node.right);
        System.out.print(node.val + " ");
    }

    public static void main(String[] args) {
        // 构造二叉树
        TreeNode root = new TreeNode(1);
        root.left = new TreeNode(2);
        root.right = new TreeNode(3);
        root.left.left = new TreeNode(4);
        root.left.right = new TreeNode(5);

        // 前序遍历
        System.out.print("Pre-order traversal: ");
        preOrderTraversal(root);
        System.out.println();

        // 中序遍历
        System.out.print("In-order traversal: ");
        inOrderTraversal(root);
        System.out.println();

        // 后序遍历
        System.out.print("Post-order traversal: ");
        postOrderTraversal(root);
        System.out.println();
    }
}