ZA | Faith Muzondo | Module-Complexity | Sprint 2 | Implement skip list

Sprint-2/implement_skip_list/skip_list.py

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+import random
+
+class Node:
+    def __init__(self, value, level):
+        self.value = value
+        self.forward = [None] * (level + 1)  # forward pointers for each level
+
+class SkipList:
+    MAX_LEVEL = 16
+    P = 0.5  # probability for random level
+
+    def __init__(self):
+        self.header = Node(None, self.MAX_LEVEL)
+        self.level = 0  # current max level in list
+
+    def random_level(self):
+        lvl = 0
+        while random.random() < self.P and lvl < self.MAX_LEVEL:
+            lvl += 1
+        return lvl
+
+    def insert(self, value):
+        update = [None] * (self.MAX_LEVEL + 1)
+        current = self.header
+
+        # Move down from top level to bottom to find insert positions
+        for i in reversed(range(self.level + 1)):
+            while current.forward[i] and current.forward[i].value < value:
+                current = current.forward[i]
+            update[i] = current
+
+        current = current.forward[0]
+
+        # Insert only if not already present
+        if current is None or current.value != value:
+            lvl = self.random_level()
+            if lvl > self.level:
+                for i in range(self.level + 1, lvl + 1):
+                    update[i] = self.header
+                self.level = lvl
+
+            new_node = Node(value, lvl)
+            for i in range(lvl + 1):
+                new_node.forward[i] = update[i].forward[i]
+                update[i].forward[i] = new_node
+
+    def contains(self, value):
+        current = self.header
+        for i in reversed(range(self.level + 1)):
+            while current.forward[i] 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.header.forward[0]
+        while current:
+            result.append(current.value)
+            current = current.forward[0]
+        return result
+
+    # Make SkipList iterable
+    def __iter__(self):
+        current = self.header.forward[0]
+        while current:
+            yield current.value
+            current = current.forward[0]