add linkedlist node_swap

Author: priyankchheda

linked_list/node_swap.py

@@ -0,0 +1,82 @@
+""" Swap two nodes in a linked list
+    input: 1 -> 5 -> 2 -> 3 -> 7 -> 9 -> 10
+    output: 1 -> 7 -> 2 -> 3 -> 5 -> 9 -> 10
+"""
+
+class Node:
+    """ Node class contains everything related to Linked List node """
+    def __init__(self, data):
+        """ initializing single node with data """
+        self.data = data
+        self.next = None
+
+
+class LinkedList:
+    """ Singly Linked List is a linear data structure """
+    def __init__(self):
+        """ initializing singly linked list with zero node """
+        self.head = None
+
+    def insert_head(self, data):
+        """ inserts node at the start of linked list """
+        node = Node(data)
+        node.next = self.head
+        self.head = node
+
+    def print(self):
+        """ prints entire linked list without changing underlying data """
+        current = self.head
+        while current is not None:
+            print(" ->", current.data, end="")
+            current = current.next
+        print()
+
+
+    def swap_node(self, node1, node2):
+        """ swap node1 with node2 """
+        previous1 = None
+        current1 = self.head
+        while current1 is not None:
+            if current1 is node1:
+                break
+            previous1 = current1
+            current1 = current1.next
+
+        previous2 = None
+        current2 = self.head
+        while current2 is not None:
+            if current2 is node2:
+                break
+            previous2 = current2
+            current2 = current2.next
+
+        if previous1 is not None:
+            previous1.next = current2
+        else:
+            self.head = current2
+        if previous2 is not None:
+            previous2.next = current1
+        else:
+            self.head = current1
+
+        current1.next, current2.next = current2.next, current1.next
+
+
+def main():
+    """ operational function """
+    linkedlist = LinkedList()
+    linkedlist.insert_head(10)
+    linkedlist.insert_head(9)
+    linkedlist.insert_head(7)
+    linkedlist.insert_head(3)
+    linkedlist.insert_head(2)
+    linkedlist.insert_head(5)
+    linkedlist.insert_head(1)
+
+    linkedlist.print()
+    linkedlist.swap_node(linkedlist.head.next, linkedlist.head.next.next.next.next)
+    linkedlist.print()
+
+
+if __name__ == '__main__':
+    main()