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> stack = new Stack<>();
        ArrayList<Integer> list = new ArrayList<>();
        TreeNode cur = root;  //用一个指针
        while(cur != null || !stack.isEmpty()){
                if(cur != null){
                    stack.push(cur);
                    cur = cur.left;
                    
                }else{
                    cur = stack.pop();
                    list.add(cur.val);
                    cur = cur.right;
                }
        }

        int []arr = new int[list.size()];
        for(int i = 0 ; i < list.size() ; i++){
            arr[i] = list.get(i);
        }
        return arr; 
        
    }
}