Data Structure Binary Tree: Level order traversal in spiral form

http://www.geeksforgeeks.org/level-order-traversal-in-spiral-form/
 1 #include <iostream>
 2 #include <vector>
 3 #include <algorithm>
 4 #include <queue>
 5 #include <stack>
 6 using namespace std;
 7 
 8 struct node {
 9     int data;
10     struct node *left, *right;
11     node() : data(0), left(NULL), right(NULL) { }
12     node(int d) : data(d), left(NULL), right(NULL) { }
13 };
14 
15 void print(node *node) {
16     if (!node) return;
17     print(node->left);
18     cout << node->data << " ";
19     print(node->right);
20 }
21 
22 void printspiral(node* root) {
23     if (!root) return;
24     bool flag = true;
25     stack<node*> S, T;
26     S.push(root);
27     while (!S.empty()) {
28         while (!S.empty()) {
29             node *top = S.top();
30             S.pop();
31             cout << top->data << " ";
32             if (!flag) {
33                 if (top->left) T.push(top->left);
34                 if (top->right) T.push(top->right);
35             }
36             else {
37                 if (top->right) T.push(top->right);
38                 if (top->left) T.push(top->left);
39             }
40         }
41         swap(S, T);
42         flag = !flag;
43     }
44 }
45 
46 
47 int main() {
48     struct node* root = new node(1);
49     root->left = new node(2);
50     root->right = new node(3);
51     root->left->left = new node(7);
52     root->left->right = new node(6);
53     root->right->left = new node(5);
54     root->right->right = new node(4);
55     printspiral(root);
56     return 0;
57 }