binary-tree-inorder-traversal[中序遍历]

题目描述

Given a binary tree, return the inorder traversal of its nodes' values.
For example:
Given binary tree{1,#,2,3},

实例

return[1,3,2].

• 思路
  中序遍历二叉树并用链表保留结果返回。
  第一种方法是递归；第二种方法是非递归。具体见代码，刚开始非递归没写对！
  附加：后序遍历非递归写法

/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
import java.util.ArrayList;
import java.util.Stack;
public class Solution {
    public ArrayList inorderTraversal(TreeNode root) {
        ArrayList list = new ArrayList();
        if(root == null)
            return list;
        
        //非递归
        Stack stack = new Stack();
        TreeNode node = root;
        while(stack.isEmpty() == false || node != null){
            while(node != null){
                stack.push(node);
                node = node.left;
            }
            
            node = stack.pop();
            list.add(node.val);
            node = node.right;
        }
        
        //递归
        //getList(root, list);
        
        return list;
    }
    
    public void getList(TreeNode node, ArrayList list){
        if(node != null){
            getList(node.left, list);
            list.add(node.val);
            getList(node.right, list);
        }
    }
}