Implement skip list insert, search, and to_list methods

Author: Fithi-Teklom

Sprint-2/implement_skip_list/skip_list.py

@@ -0,0 +1,75 @@
+
+import random
+
+class Node:
+    __slots__ = ("value", "forward")
+
+    def __init__(self, value: int, level: int) -> None:
+        self.value = value
+        self.forward = [None] * (level + 1)
+
+
+class SkipList:
+    def __init__(self) -> None:
+        self.max_level = 4
+        self.level = 0
+        self.head = Node(0, self.max_level)
+    
+    def _random_level(self) -> int:
+        level = 0
+
+        while level < self.max_level and random.random() < 0.5:
+            level += 1
+
+        return level
+    def insert(self, value: int) -> None:
+        update = [self.head] * (self.max_level + 1)
+        current = self.head
+
+        for level in range(self.level, -1, -1):
+            while current.forward[level] is not None:
+                if current.forward[level].value < value:
+                    current = current.forward[level]
+                else:
+                    break
+
+            update[level] = current
+
+        node_level = self._random_level()
+        new_node = Node(value, node_level)
+ 
+        if node_level > self.level:
+            for i in range(self.level + 1, node_level + 1):
+                update[i] = self.head
+                self.level = node_level
+
+        for i in range(node_level + 1):
+            new_node.forward[i] = update[i].forward[i]
+            update[i].forward[i] = new_node
+
+    def contains(self, value: int | str) -> bool:
+        current = self.head
+
+        for level in range(self.level, -1, -1):
+            while current.forward[level] is not None:
+                if current.forward[level].value < value:
+                    current = current.forward[level]
+                else:
+                    break
+
+        current = current.forward[0]
+
+        return current is not None and current.value == value
+
+    def __contains__(self, value: int | str) -> bool:
+        return self.contains(value)
+
+    def to_list(self) -> list[int | str]:
+        result = []
+        current = self.head.forward[0]
+
+        while current is not None:
+            result.append(current.value)
+            current = current.forward[0]
+
+        return result