Glasgow | Prati Amalden | 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.next = [None] * (level + 1) # next[i] the next node at level i
+
+
+class SkipList:
+    MAX_LEVEL = 16
+    P = 0.5
+
+    def __init__(self):
+        self.head = Node(None, self.MAX_LEVEL)
+        self.level = 0          # highest level currently in use
+
+    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.head
+
+        # Find the place where the new value should go
+        for level in range(self.level, -1, -1):
+            while current.next[level] and current.next[level].value < value:
+                current = current.next[level]
+            update[level] = current
+
+        next_node = current.next[0]
+        if next_node and next_node.value == value:
+            return
+
+        node_level = self._random_level()
+
+        if node_level > self.level:
+            for level in range(self.level + 1, node_level + 1):
+                update[level] = self.head
+            self.level = node_level
+
+        new_node = Node(value, node_level)
+        for level in range(node_level + 1):
+            new_node.next[level] = update[level].next[level]
+            update[level].next[level] = new_node
+
+    # Check if value exists
+    def contains(self, value):
+        current = self.head
+        for level in range(self.level, -1, -1):
+            while current.next[level] and current.next[level].value < value:
+                current = current.next[level]
+
+        candidate = current.next[0]
+        return candidate is not None and candidate.value == value
+
+    def __contains__(self, value):
+        return self.contains(value)
+
+    def to_list(self):
+        result = []
+        current = self.head.next[0]
+        while current:
+            result.append(current.value)
+            current = current.next[0]
+        return result
+
+