LeetCode | Binary Tree Level Order Traversal II

Given a binary tree, return the bottom-up level order traversal of its nodes' values. (ie, from left to right, level by level from leaf to root).

For example:
Given binary tree {3,9,20,#,#,15,7},

    3   / \  9  20    /  \   15   7

return its bottom-up level order traversal as:

[  [15,7],  [9,20],  [3]]

confused what "{1,#,2,3}" means? > read 

思路：与Binary Tree Level Order Traversal这题一致，就是将最后的结果倒置一下即可。

class Solution {public:    vector<vector<int> > levelOrderBottom(TreeNode *root) {queue<TreeNode*> L;TreeNode* temp;vector<int>v;vector<TreeNode*>vt;vector<vector<int> >vv;if(root){v.push_back(root->val);vv.push_back(v);}L.push(root);while(!L.empty()){temp = L.front();vt.push_back(temp);L.pop();if(!temp)continue;L.push(temp->left);L.push(temp->right);}int i,j,cnt=0;int step = 3;for(i=1; i<vt.size(); i=j){v.clear();for(j=i; j<step && j<vt.size(); j++){if(vt[j]!=NULL){v.push_back(vt[j]->val);cnt+=2;}}step = j+cnt;cnt = 0;if(j<vt.size())vv.push_back(v);}reverse(vv.begin(), vv.end());//结果倒置        return vv;    }};