leetcode-94. Binary Tree Inorder Traversal

题目：

Given a binary tree, return the inorder traversal of its nodes’ values.

For example:
Given binary tree [1,null,2,3],
1
\
2
/
3
return [1,3,2].

二叉树的前序遍历，这里用的FIFO列表，和一个tmp指针。

/** * Definition for a binary tree node. * public class TreeNode { *     int val; *     TreeNode left; *     TreeNode right; *     TreeNode(int x) { val = x; } * } */public class Solution {    public List<Integer> inorderTraversal(TreeNode root) {        LinkedList<TreeNode> list = new LinkedList<TreeNode>();        List<Integer> ret = new ArrayList<Integer>();        TreeNode tmp = root;        while(tmp!=null || list.size()>0){            while(tmp != null){                list.add(tmp);                tmp = tmp.left;            }            tmp = list.removeLast();            ret.add(tmp.val);            tmp = tmp.right;        }        return ret;    }}