Day 33 Merge sort of linked list

Author: mandliya

README.md

@@ -4,9 +4,9 @@
 
 | Current Status|     Stats     |
 | :------------: | :----------: |
-| Total Problems | 48 |
-| Current Streak | 31 |
-| Longest Streak | 31 ( August 17, 2015 - September 16, 2015 ) |
+| Total Problems | 50 |
+| Current Streak | 33 |
+| Longest Streak | 33 ( August 17, 2015 - September 18, 2015 ) |
 
 </center>
 
@@ -25,6 +25,8 @@
 | Determine the intersection(merging) point of two given linked list.| [findIntersectionPointOfLists.cpp](linked_list_problems/findIntersectionPointOfLists.cpp)|
 | Clone a linkedlist which has next and an random pointer, Space Complexity - O(1). | [cloneListWithRandomPtr.cpp](linked_list_problems/cloneListWithRandomPtr.cpp)|
 | Given a sorted linked list with duplicates, remove duplicates in one iteration. | [removeDuplicatesFromSortedList.cpp](linked_list_problems/removeDuplicatesFromSortedList.cpp)| 
+| Find the nth node of linked list from last. | [nthToLastNode.cpp] (linked_list_problems/nthToLastNode.cpp) |
+| Sort a linked list using merge sort | [merge_sort.cpp] (linked_list_problems/merge_sort.cpp) |
 
 ### Include 
 Include contains single header implementation of data structures and some algorithms.

linked_list_problems/merge_sort.cpp

@@ -0,0 +1,122 @@
+#include <iostream>
+
+struct Node {
+  int data;
+  Node * next;
+  Node ( int d ) : data{ d }, next{ nullptr } { }
+};
+
+void printList( Node * head ) {
+  while( head ) {
+    std::cout << head->data << "-->";
+    head = head->next;
+  }
+  std::cout << "NULL" << std::endl;
+}
+
+void push( Node * & head, int data )
+{
+  Node * newNode = new Node(data);
+  if ( head == nullptr ) {
+    head = newNode;
+  } else {
+    Node * temp = head;
+    while ( temp->next != nullptr ) {
+      temp = temp->next;
+    }
+    temp->next = newNode;
+  }
+}
+
+void splitList( Node * head, Node * & list1, Node * & list2 )
+{
+  if ( head == nullptr || head->next == nullptr ) {
+    list1 = head;
+    list2 = nullptr;
+    return;
+  }
+  Node * fast = head->next;
+  Node * slow = head;
+  while( fast ) {
+    fast = fast->next;
+    if( fast ) {
+      slow = slow->next;
+      fast = fast->next;
+    }
+  }
+  list1 = head;
+  list2 = slow->next;
+  slow->next = nullptr;
+}
+
+
+void moveNode( Node * & dstNode, Node * & srcNode )
+{
+  if (srcNode == nullptr) {
+    return;
+  }
+  Node * nextNode = srcNode->next;
+  dstNode->next = srcNode;
+  dstNode = srcNode;
+  srcNode = nextNode;
+}
+
+
+Node * sortedMerge(Node * list1, Node * list2)
+{
+  if (list1 == nullptr) {
+    return list2;
+  }
+
+  if (list2 == nullptr) {
+    return list1;
+  }
+
+  Node dummy(0);
+  Node * tailNode = &dummy;
+  dummy.next = nullptr;
+
+  while( list1 && list2 ) {
+    if (list1->data <= list2->data){
+      moveNode(tailNode, list1);
+    } else {
+      moveNode(tailNode, list2);
+    }
+  }
+  while(list2) {
+    moveNode(tailNode, list2);
+  }
+  while(list1) {
+    moveNode(tailNode, list1);
+  }
+  return (dummy.next);
+}
+
+void mergeSort( Node * & head ) {
+  if (head == nullptr || head->next == nullptr) {
+    return;
+  }
+  Node * list1 = nullptr;
+  Node * list2 = nullptr;
+  splitList(head, list1, list2);
+  mergeSort(list1);
+  mergeSort(list2);
+  head = sortedMerge(list1, list2);
+}
+
+int main()
+{
+  Node * head = nullptr;
+  push(head, 5);
+  push(head, 1);
+  push(head, 3);
+  push(head, 6);
+  push(head, 4);
+  push(head, 2);
+  std::cout << "Before Sorting :";
+  printList(head);
+  mergeSort(head);
+  std::cout << "After Sorting  :";
+  printList(head);
+  return 1;
+}