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) {
        if(root == null) return new int[0];
        
        int[] l = new int[0];
        if(root.left != null) {
            l = inorderTraversal(root.left);
        } 
        int[] r = new int[0];
        if(root.right != null) {
            r = inorderTraversal(root.right);
        } 

        int[] re = new int[1 + l.length + r.length];

        for(int i = 0; i < l.length; i++) {
            re[i] = l[i];
        }
        re[l.length] = root.val;
        for(int i = 0; i < r.length; i++) {
            re[i+1+l.length] = r[i];
        }
        return re;
    }
}