Data Structure Linked List: Flattening a Linked List

http://www.geeksforgeeks.org/flattening-a-linked-list/

 1 #include <iostream>

 2 #include <vector>

 3 #include <algorithm>

 4 #include <queue>

 5 #include <stack>

 6 #include <string>

 7 #include <fstream>

 8 #include <map>

 9 #include <set>

10 using namespace std;

11 

12 struct node {

13     int data;

14     node *right;

15     node *down;

16     node(int d = 0) : data(d), right(NULL), down(NULL) { }

17 };

18 

19 struct cmp {

20     bool operator() (node *a, node *b) {

21         return a->data > b->data;

22     }

23 };

24 

25 void push(node* &head, int k) {

26     node *new_node = new node(k);

27     new_node->down = head;

28     head = new_node;

29 }

30 

31 node* flatten(node *&root) {

32     priority_queue<node*, vector<node*>, cmp> S;

33     while (root) {

34         S.push(root);

35         root = root->right;

36     }

37     root = NULL;

38     node *p;

39     while (!S.empty()) {

40         node *top = S.top();

41         S.pop();

42         if (!root) {

43             root = top;

44             p = top;

45         }

46         else {

47             p->right = top;

48             p = p->right;

49         }

50         if (top->down) S.push(top->down);

51     }

52     return root;

53 }

54 

55 void print(node *head) {

56     while (head) {

57         cout << head->data << " ";

58         head = head->right;

59     }

60 }

61 

62 int main() {

63     node *root = NULL;

64     push( root, 30 );

65     push( root, 8 );

66     push( root, 7 );

67     push( root, 5 );

68 

69     push( ( root->right ), 20 );

70     push( ( root->right ), 10 );

71 

72     push( ( root->right->right ), 50 );

73     push( ( root->right->right ), 22 );

74     push( ( root->right->right ), 19 );

75 

76     push( ( root->right->right->right ), 45 );

77     push( ( root->right->right->right ), 40 );

78     push( ( root->right->right->right ), 35 );

79     push( ( root->right->right->right ), 20 );

80 

81     root = flatten(root);

82     print(root);

83     return 0;

84 }