Binary Tree Zigzag Level Order Traversal 【leetcode】

/**
* Definition for binary tree
* struct TreeNode {
*     int val;
*     TreeNode *left;
*     TreeNode *right;
*     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
vector<vector<int> > zigzagLevelOrder(TreeNode *root) {
vector<vector<int> > v;
vector<int> vv;
if(!root)return v;
stack<TreeNode*>a,b;
int i,j,k=1;
a.push(root);

while(!a.empty())
{
TreeNode* temp=a.top();
a.pop();
vv.push_back(temp->val);
if(k)
{
if(temp->left)b.push(temp->left);
if(temp->right)b.push(temp->right);
}
else
{
if(temp->right)b.push(temp->right);
if(temp->left)b.push(temp->left);
}

if(a.empty())
{
v.push_back(vv);
vv.clear();
k=(k+1)&1;
swap(a,b);
}
}
return v;
}
};