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> arr = new ArrayList<Integer>();

        if (root != null) {
            if (root.left != null) {
                travel(root.left, arr);
            }
            arr.add(root.val);
            if (root.right != null) {
                travel(root.right, arr);
            }
        }
        int[] arrInt = new int[arr.size()];
        for (int i = 0; i < arrInt.length; i++) {
            arrInt[i] = arr.get(i);
        }
        return arrInt;
    }
    public void travel(TreeNode root, ArrayList<Integer> arr) {
        if (root != null) {
            if (root.left != null) {
                travel(root.left, arr);
            }
            arr.add(root.val);
            if (root.right != null) {
                travel(root.right, arr);
            }
        }
    }
}