[Lintcode] #70 二叉树的层次遍历 II

给出一棵二叉树，返回其节点值从底向上的层次序遍历（按从叶节点所在层到根节点所在的层遍历，然后逐层从左往右遍历）

/** * Definition of TreeNode: * public class TreeNode { *     public int val; *     public TreeNode left, right; *     public TreeNode(int val) { *         this.val = val; *         this.left = this.right = null; *     } * } */public class Solution {    /*     * @param root: A tree     * @return: buttom-up level order a list of lists of integer     */    public List<List<Integer>> levelOrderBottom(TreeNode root) {        // write your code here        LinkedList<List<Integer>> re = new LinkedList<>();LinkedList<TreeNode> stack = new LinkedList<>();if (root == null)return re;stack.add(root);while (!stack.isEmpty()) {int n = stack.size();List<Integer> temp = new ArrayList<>();while (n-- > 0) {TreeNode cur = stack.poll();temp.add(cur.val);if (cur.left != null)stack.add(cur.left);if (cur.right != null)stack.add(cur.right);}re.addFirst(temp);}return re;    }}