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
        Stack<TreeNode> sta = new Stack<>();
        List<Integer> res = new ArrayList<>();
        while (!sta.empty() || root != null) {
            while (root != null) {
                sta.push(root);
                root = root.left;
            }
            TreeNode tmp = sta.pop();
            res.add(tmp.val);
            root = tmp.right;
        }
        return res.stream().mapToInt(Integer::intValue).toArray();
    }
}