二叉树的遍历java递归

二叉树的遍历有三种方式：前序遍历、中序遍历和后序遍历。下面是使用Java递归进行二叉树遍历的代码示例：

前序遍历：

import java.util.ArrayList;
import java.util.List;

public class Solution {
    public static void main(String[] args) {
        TreeNode node1 = new TreeNode(1);
        node1.right = new TreeNode(3);
        Solution sol = new Solution();
        System.out.println(sol.preorderTraversal(node1));
    }

    public List<Integer> preorderTraversal(TreeNode root) {
        List<Integer> list = new ArrayList<Integer>();
        preOrder(list, root);
        return list;
    }

    public void preOrder(List<Integer> list, TreeNode root) {
        if (root == null) {
            return;
        }
        list.add(root.val);
        preOrder(list, root.left);
        preOrder(list, root.right);
    }
}

中序遍历：

import java.util.ArrayList;
import java.util.List;

public class Solution {
    public static void main(String[] args) {
        Solution sol = new Solution();
        TreeNode node1 = new TreeNode(1);
        node1.left = new TreeNode(2);
        node1.right = new TreeNode(3);
        node1.right.left = new TreeNode(4);
        System.out.println(sol.inorderTraversal(node1));
    }

    public List<Integer> inorderTraversal(TreeNode root) {
        List<Integer> list = new ArrayList<Integer>();
        inOrder(list, root);
        return list;
    }

    public void inOrder(List<Integer> list, TreeNode root) {
        if (root == null) {
            return;
        }
        inOrder(list, root.left);
        list.add(root.val);
        inOrder(list, root.right);
    }
}

后序遍历：

import java.util.ArrayList;
import java.util.List;

public class Solution {
    public static void main(String[] args) {
        Solution sol = new Solution();
        TreeNode node = new TreeNode(1);
        node.left = new TreeNode(2);
        node.right = new TreeNode(3);
        System.out.println(sol.postorderTraversal(node));
    }

    public List<Integer> postorderTraversal(TreeNode root) {
        List<Integer> list = new ArrayList<Integer>();
        postOrder(list, root);
        return list;
    }

    public void postOrder(List<Integer> list, TreeNode root) {
        if (root == null) {
            return;
        }
        postOrder(list, root.left);
        postOrder(list, root.right);
        list.add(root.val);
    }
}