feat: add algo to group odd even nodes in a Linked List

Adding the algorithm I used to solve
https://leetcode.com/problems/odd-even-linked-list/

This groups odd indexed nodes in a Linked List at the beginning of the
list and then the even indexed nodes following the odd indexed nodes.

Note that the nodes are not grouped by their value but by their
index. This algo runs in O(1) space and O(n) time.

Author: shermanhui

Diff for: data_structures/linked_list/group_odd_even_nodes.py

@@ -0,0 +1,143 @@
+"""
+`group_odd_even_nodes` will group all odd indexed nodes at the beginning
+of the list and all even indexed nodes following the odd indexed nodes.
+
+- This will run in O(1) space and O(n) time
+- Groups by index and **NOT** the value of the node
+- Will return the head if there is one or none elements in the Linked List
+"""
+
+
+class Node:
+    def __init__(self, data=None, next=None):
+        self.data = data
+        self.next = next
+
+    def __repr__(self):
+        """Returns a visual representation of the node and all its
+        following nodes."""
+        string_rep = []
+        temp = self
+        while temp:
+            string_rep.append(f"{temp.data}")
+            temp = temp.next
+        return "->".join(string_rep)
+
+
+class LinkedList:
+    """
+    >>> linked_list = LinkedList()
+    >>> linked_list.group_odd_even_nodes()
+
+    >>> linked_list.insert(5)
+    >>> linked_list.group_odd_even_nodes()
+    5
+    >>> linked_list.insert(7)
+    >>> linked_list.group_odd_even_nodes()
+    7->5
+    >>> linked_list.insert(8)
+    >>> linked_list.group_odd_even_nodes()
+    8->5->7
+    >>> linked_list.clear_list()
+    >>> linked_list.insert(5)
+    >>> linked_list.insert(7)
+    >>> linked_list.insert(8)
+    >>> linked_list.insert(9)
+    >>> linked_list.group_odd_even_nodes()
+    9->7->8->5
+    >>> linked_list.clear_list()
+    >>> linked_list.insert(5)
+    >>> linked_list.insert(7)
+    >>> linked_list.insert(8)
+    >>> linked_list.insert(9)
+    >>> linked_list.insert(2)
+    >>> linked_list.group_odd_even_nodes()
+    2->8->5->9->7
+    """
+
+    def __init__(self):
+        self.head = None
+
+    def __iter__(self):
+        node = self.head
+
+        while node:
+            yield node.data
+            node = node.next
+
+    def __repr__(self):
+        """
+        String representation/visualization of a Linked Lists
+        """
+        return "->".join([str(item) for item in self])
+
+    def insert(self, data):
+        new_node = Node(data)
+
+        if self.is_empty():
+            self.head = new_node
+        else:
+            self.head = Node(data, self.head)
+
+    def remove(self, data):
+        if self.is_empty():
+            return "Linked List is empty"
+        else:
+            prev, current = None, self.head
+            while current:
+                if current.data == data:
+                    if prev:
+                        prev.next = current.next
+                        current = prev
+                    else:
+                        self.head = self.head.next
+                else:
+                    prev = current
+                current = current.next
+            return self.head
+
+    def is_empty(self):
+        return self.head is None
+
+    def group_odd_even_nodes(self):
+        if not self.head or not self.head.next:
+            return self.head
+
+        odd = self.head
+        even = self.head.next
+
+        while even and even.next:
+            temp = even.next
+            even.next = even.next.next
+
+            temp.next = odd.next
+            odd.next = temp
+
+            odd = odd.next
+            even = even.next
+
+        return self.head
+
+    def clear_list(self):
+        self.head = None
+
+
+def main():
+    from doctest import testmod
+
+    testmod()
+
+    linked_list = LinkedList()
+    linked_list.insert(5)
+    linked_list.insert(7)
+    linked_list.insert(8)
+    linked_list.insert(9)
+    linked_list.insert(2)
+    print(linked_list)  # expect 2->9->8->7->5
+
+    linked_list.group_odd_even_nodes()
+    print(linked_list)  # expect 2->8->5->9->7
+
+
+if __name__ == "__main__":
+    main()