题解 | #二叉树的中序遍历#

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
     */
    public int[] inorderTraversal(TreeNode root) {
        // write code here
        ArrayList<Integer> result = new ArrayList<>();

        preorderTraversal(root, result);
        int[] ints = new int[result.size()];
        for (int i = 0; i < result.size(); i++) {
            ints[i] = result.get(i);
        }
        return ints;
    }

    public void preorderTraversal(TreeNode root, ArrayList<Integer> result) {
        if (root == null) {
            return;
        }
        preorderTraversal(root.left, result);
        result.add(root.val);
        preorderTraversal(root.right, result);

    }
}