LintCode 70 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:
 * class TreeNode {
 * public:
 *     int val;
 *     TreeNode *left, *right;
 *     TreeNode(int val) {
 *         this->val = val;
 *         this->left = this->right = NULL;
 *     }
 * }
 */

class Solution {
public:
    /**
     * @param root: A tree
     * @return: buttom-up level order a list of lists of integer
     */

    vector> levelOrderBottom(TreeNode * root) {
        vector> ans,ans1;
        vector node;
        vector layernum;
        vector layer;
        int front=0;
        if(root==NULL) return ans1;
        node.push_back(root);
        layernum.push_back(0);
        while(node.size()-front>0){
            if(front!=0&&layernum[front]!=layernum[front-1]){
                ans.push_back(layer);
                layer.clear();
            }
            layer.push_back(node[front]->val);
            if(node[front]->left!=NULL){
                node.push_back(node[front]->left);
                layernum.push_back(layernum[front]+1);
            }
            if(node[front]->right!=NULL){
                node.push_back(node[front]->right);
                layernum.push_back(layernum[front]+1);
            }
            front++;
        }
        if(layer.size()!=0) ans.push_back(layer);
        for(int i=ans.size()-1;i>=0;i--){
            ans1.push_back(ans[i]);

        }
        return ans1;
    }
};