Java实现二叉树前序遍历

在 Java 中，可以通过递归或使用栈来实现二叉树的前序遍历。下面分别给出这两种方法的实现示例：

递归实现前序遍历：

class TreeNode {int val;TreeNode left;TreeNode right;TreeNode(int val) {this.val = val;this.left = null;this.right = null;}
}public class BinaryTreeTraversal {// 前序遍历递归函数public void preOrderTraversal(TreeNode root) {if (root == null) {return;}System.out.print(root.val + " "); // 先访问根节点preOrderTraversal(root.left); // 递归遍历左子树preOrderTraversal(root.right); // 递归遍历右子树}public static void main(String[] args) {// 创建二叉树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);// 创建 BinaryTreeTraversal 对象BinaryTreeTraversal traversal = new BinaryTreeTraversal();// 调用前序遍历方法System.out.print("前序遍历结果: ");traversal.preOrderTraversal(root);}
}

使用栈实现前序遍历：

import java.util.Stack;class TreeNode {int val;TreeNode left;TreeNode right;TreeNode(int val) {this.val = val;this.left = null;this.right = null;}
}public class BinaryTreeTraversal {// 使用栈实现前序遍历public void preOrderTraversal(TreeNode root) {if (root == null) {return;}Stack<TreeNode> stack = new Stack<>();stack.push(root);while (!stack.isEmpty()) {TreeNode node = stack.pop();System.out.print(node.val + " "); // 先访问当前节点// 先将右子树压入栈，再将左子树压入栈，这样出栈时会先处理左子树if (node.right != null) {stack.push(node.right);}if (node.left != null) {stack.push(node.left);}}}public static void main(String[] args) {// 创建二叉树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);// 创建 BinaryTreeTraversal 对象BinaryTreeTraversal traversal = new BinaryTreeTraversal();// 调用前序遍历方法System.out.print("前序遍历结果: ");traversal.preOrderTraversal(root);}
}