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#include <iostream>
#include <cstdio>
#include <string>
#include <cstdlib>
#include <fstream>
using namespace std;
struct node
{
string data;
int num;
struct node* next;
};
struct node* SortedMerge(node* a, node* b);
void FrontBackSplit(node* source, node** frontRef, node** backRef);
/* sorts the linked list by changing next pointers (not data) */
void MergeSort(struct node** headRef)
{
node* head = *headRef;
node* a;
node* b;
if ((head == NULL) || (head->next == NULL))
{
return;
}
FrontBackSplit(head, &a, &b);
/*MergeSort(&a);
MergeSort(&b);*/
*headRef = SortedMerge(a, b);
}
/* merge the sorted linked lists */
node* SortedMerge(struct node* a, struct node* b)
{
node* result = NULL;
if (a == NULL)
return b;
else if (b==NULL)
return a;
if (a->data <= b->data)
{
result = a;
result->next = SortedMerge(a->next, b);
}
else
{
result = b;
result->next = SortedMerge(a, b->next);
}
return result;
}
/* Split the nodes of the given list into front and back halves*/
void FrontBackSplit(node* source, node** frontRef, node** backRef)
{
node* fast;
node* slow;
if (source==NULL || source->next==NULL)
{
*frontRef = source;
*backRef = NULL;
}
else
{
slow = source;
fast = source->next;
while (fast != NULL)
{
fast = fast->next;
if (fast != NULL)
{
slow = slow->next;
fast = fast->next;
}
}
*frontRef = source;
*backRef = slow->next;
slow->next = NULL;
}
}
/* print nodes in a given linked list */
void printList(node *node)
{
while (node != NULL)
{
cout<<node->data<<endl;
node = node->next;
}
}
/* insert a node at the beginging of the linked list */
void push(node** head_ref, string new_data)
{
node *new_node = new node;
new_node->data = new_data;
new_node->next = (*head_ref);
(*head_ref) = new_node;
}
/* Main */
int main()
{
int num;
string file_name;
string file;
ifstream infile;
node* res = NULL;
node* a = NULL;
cout << "What file would you like to open: ";
getline(cin, file_name);
infile.open(file_name);
while(infile >> num && (getline(infile, file)))
{
push(&a, file);
}
MergeSort(&a);
cout<<"\n Sorted Linked List is: \n";
printList(a);
system("Pause");
return 0;
}
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