题解 | #二叉树的中序遍历#

简单递归解决中序遍历

import java.util.*;

/*
 * public class TreeNode {
 *   int val = 0;
 *   TreeNode left = null;
 *   TreeNode right = null;
 *   public TreeNode(int val) {
 *     this.val = val;
 *   }
 * }
 */

public class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @param root TreeNode类 
     * @return int整型一维数组
     */
    ArrayList<Integer> list = new ArrayList<>();

    public int[] inorderTraversal (TreeNode root) {
        // write code here
        inorder(root);


        int[] res = new int[list.size()];

        int index = 0;

        for (int num : list) {
            res[index] = list.get(index++);
        }

        return res;
    }

    private void inorder(TreeNode node) {
        if (node != null) {
            inorder(node.left);
            list.add(node.val);
            inorder(node.right);
        }
    }
}