Data Structure Binary Tree: Populate Inorder Successor for all nodes

http://www.geeksforgeeks.org/populate-inorder-successor-for-all-nodes/

 1 #include <iostream>
 2 #include <vector>
 3 #include <algorithm>
 4 #include <queue>
 5 #include <stack>
 6 #include <string>
 7 #include <fstream>
 8 using namespace std;
 9 
10 struct node {
11     int data;
12     struct node *left, *right, *next;
13     node() : data(0), left(NULL), right(NULL), next(NULL) { }
14     node(int d) : data(d), left(NULL), right(NULL), next(NULL) { }
15 };
16 
17 void populate(node *root) {
18     static node *next = NULL;
19     if (!root) return;
20     populate(root->right);
21     root->next = next;
22     next = root;
23     populate(root->left);
24 }
25 
26 int main() {
27     node *root = new node(10);
28     root->left = new node(8);
29     root->right = new node(12);
30     root->left->left = new node(3);
31     populate(root);
32     cout << root->data << "->" << (root->next? root->next->data : -1) << endl;
33     cout << root->left->data << "->" << (root->left->next? root->left->next->data : -1) << endl;
34     cout << root->right->data << "->" << (root->right->next? root->right->next->data : -1) << endl;
35     cout << root->left->left->data << "->" << (root->left->left->next? root->left->left->next->data : -1) << endl;
36     return 0;
37 }