题解 | #二叉树的中序遍历#

import java.util.*;

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) {
        Stack<TreeNode> stack = new Stack<>();
        List<Integer> list = new ArrayList<>();
        stack.add(root);
        while(!stack.isEmpty()){
            TreeNode pop = stack.pop();
            if(pop!=null){
                stack.add(pop);
                stack.add(pop.left);
            }else if(!stack.isEmpty()){
                TreeNode pop1 = stack.pop();
                list.add(pop1.val);
                stack.add(pop1.right);
            }
        }
        int[] result = new int[list.size()];
        for (int i = 0; i < list.size(); i++) {
            result[i] = list.get(i);
        }
        return result;
    }
}