Zigzag tree traversal

// zigzag trav for tree

            --->
//           12
//         /    \
        <------------
//        9      15
//       / \
      ------------>
//      4   10

// output :- 12 15 9 4 10

#include<iostream>
#include<stack>
using namespace std;
class Node
{
public:
    int data;
    Node *right,*left;
    Node(int data)
    {
        this->data=data;
        right=left=NULL;
    }
};
void zigzagtrav(Node *root)
{
    stack<Node*> curr;
    stack<Node*> next;
    bool leftToright=true;
    curr.push(root);
    while(!curr.empty())
    {
        Node *tmp=curr.top();
        curr.pop();
        if(tmp)
        {
            cout<<tmp->data<<" ";
            if(leftToright)
            {
                next.push(tmp->left);
                next.push(tmp->right);
            }
            else
            {
                next.push(tmp->right);
                next.push(tmp->left);
            }
        }
        if(curr.empty())
        {
            leftToright=!leftToright;
            swap(curr,next);
        }
    }
}
int main()
{   
    #ifndef ONLINE_JUDGE
        freopen("../input.txt", "r", stdin);
        freopen("../output.txt", "w", stdout);
    #endif
    Node *root=new Node(12);
    root->right=new Node(15);
    root->left=new Node(9);
    root->left->left=new Node(4);
    root->left->right=new Node(10);
    zigzagtrav(root);
    return 0;
}