Add py linked list

Author: awpala

python/data_structures/p238_linked_list.py

@@ -0,0 +1,27 @@
+'''
+    CLRS Section 10.2, p. 238
+'''
+class LinkedList:
+    def __init__(self, head=None):
+        self.head = head
+    
+    def list_search(self, k):
+        x = self.head
+        while x is not None and x.key != k:
+            x = x.next
+        return x
+    
+    def list_insert(self, x):
+        x.next = self.head
+        if self.head is not None:
+            self.head.prev = x
+        self.head = x
+        x.prev = None
+    
+    def list_delete(self, x):
+        if x.prev is not None:
+            x.prev.next = x.next
+        else:
+            self.head = x.next
+        if x.next is not None:
+            x.next.prev = x.prev

python/main.py

@@ -4,7 +4,7 @@
 '''
 
 # import utilities (ADTs)
-from utilities import A
+from utilities import A, ListNode
 
 # ----- SORTING ALGORITMS ----- #
 print('\n|----- SORTING ALGORITHMS ----|')
@@ -233,3 +233,32 @@
 print('after head_enqueue(8):', Q.Q)
 Q.tail_dequeue()
 print('after tail_dequeue():', Q.Q)
+
+# CLRS Section 10.2 - Linked List
+from data_structures.p238_linked_list import LinkedList
+
+print('\nSection 10.2 - Linked List')
+
+L = LinkedList()
+L.list_insert(ListNode(1))
+L.list_insert(ListNode(4))
+L.list_insert(ListNode(16))
+L.list_insert(ListNode(9)) # cf. Figure 10.3, p. 237
+L.list_insert(ListNode(25))
+print('\nafter list_insert(25):'
+    , L.head.key, '->'
+    , L.head.next.key, '->'
+    , L.head.next.next.key, '->'
+    , L.head.next.next.next.key, '->'
+    , L.head.next.next.next.next.key, '->'
+    , L.head.next.next.next.next.next
+)
+delete_node = L.list_search(4)
+L.list_delete(delete_node)
+print('after list_delete(4):'
+    , L.head.key, '->'
+    , L.head.next.key, '->'
+    , L.head.next.next.key, '->'
+    , L.head.next.next.next.key, '->'
+    , L.head.next.next.next.next
+)

python/utilities.py

@@ -9,3 +9,8 @@
 # A is a list ADT, represented by a Python list
 A = []
 
+class ListNode:
+    def __init__(self, key, prev=None, next=None):
+        self.key = key
+        self.prev = prev
+        self.next = next