Binary Tree Zigzag Level Order Traversal

Given a binary tree, return the zigzag level order traversal of its nodes' values. (ie, from left to right, then right to left for the next level and alternate between).

For example:

Given binary tree 

{3,9,20,#,#,15,7}

,

3
/ \
9  20
/  \
15   7

return its zigzag level order traversal as:

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

#include<iostream>
#include<vector>
#include<queue>
#include<map>
#include<algorithm>
using namespace std;

struct TreeNode {
int val;
TreeNode *left;
TreeNode *right;
TreeNode(int x) : val(x), left(NULL), right(NULL) {}
};

vector<vector<int> > levelOrder(TreeNode *root) {
queue<pair<TreeNode*,int> >  BFS_Queue;
vector<int> LevelVal;
vector<vector<int> > Result;

if (root == NULL)
return Result;
BFS_Queue.push(make_pair(root,0));
int Curlevel = 0;
while (!BFS_Queue.empty())
{
TreeNode* Curnode = BFS_Queue.front().first;
if (BFS_Queue.front().second != Curlevel)
{
Result.push_back(LevelVal);
LevelVal.clear();
Curlevel = BFS_Queue.front().second;
}
if (BFS_Queue.front().second%2==0)
LevelVal.push_back(Curnode->val);
else
LevelVal.insert(LevelVal.begin(),Curnode->val);
BFS_Queue.pop();
if (Curnode->left)
BFS_Queue.push(make_pair(Curnode->left, Curlevel + 1));
if (Curnode->right)
BFS_Queue.push(make_pair(Curnode->right, Curlevel + 1));
}
Result.push_back(LevelVal);
return Result;
}