London | 26-SDC-March | Zobeir Rigi | Sprint 2 | Implement a skip list

Sprint-2/implement_skip_list/skip_list.py

@@ -0,0 +1,74 @@
+import random
+
+MAX_LEVEL = 4
+
+
+class Node:
+    def __init__(self, value, level):
+        self.value = value
+        self.forward = [None] * level
+
+
+class SkipList:
+    def __init__(self):
+        self.head = Node(None, MAX_LEVEL)
+        self.level = 1
+
+    def _random_level(self):
+        level = 1
+
+        while level < MAX_LEVEL and random.random() < 0.5:
+            level += 1
+
+        return level
+
+    def insert(self, value):
+        update = [None] * MAX_LEVEL
+        current = self.head
+
+        for i in range(self.level - 1, -1, -1):
+            while (
+                current.forward[i] is not None
+                and current.forward[i].value < value
+            ):
+                current = current.forward[i]
+
+            update[i] = current
+
+        node_level = self._random_level()
+
+        if node_level > self.level:
+            for i in range(self.level, node_level):
+                update[i] = self.head
+
+            self.level = node_level
+
+        new_node = Node(value, node_level)
+
+        for i in range(node_level):
+            new_node.forward[i] = update[i].forward[i]
+            update[i].forward[i] = new_node
+
+    def __contains__(self, value):
+        current = self.head
+
+        for i in range(self.level - 1, -1, -1):
+            while (
+                current.forward[i] is not None
+                and current.forward[i].value < value
+            ):
+                current = current.forward[i]
+
+        current = current.forward[0]
+
+        return current is not None and current.value == value
+
+    def to_list(self):
+        result = []
+        current = self.head.forward[0]
+
+        while current is not None:
+            result.append(current.value)
+            current = current.forward[0]
+
+        return result