London | 26-JUL-SDC |Ping Wang | Sprint 2 | Skip list CYF-1185

Sprint-2/implement_skip_list/skip_list.py

@@ -0,0 +1,78 @@
+import random
+
+
+class Node:
+    def __init__(self, value, level):
+        self.value = value
+        self.next = [None] * level
+
+
+class SkipList:
+    MAX_LEVEL = 16
+
+    def __init__(self):
+        self.head = Node(None, self.MAX_LEVEL)
+        self.level = 1
+
+    def random_level(self):
+        level = 1
+
+        while (
+            level < self.MAX_LEVEL
+            and random.random() < 0.5
+        ):
+            level += 1
+
+        return level
+
+    def insert(self, value):
+        update = [None] * self.MAX_LEVEL
+
+        current = self.head
+
+        for level in range(self.level - 1, -1, -1):
+            while (
+                current.next[level] is not None
+                and current.next[level].value < value
+            ):
+                current = current.next[level]
+
+            update[level] = current
+
+        new_level = self.random_level()
+
+        if new_level > self.level:
+            for level in range(self.level, new_level):
+                update[level] = self.head
+
+            self.level = new_level
+
+        node = Node(value, new_level)
+
+        for level in range(new_level):
+            node.next[level] = update[level].next[level]
+            update[level].next[level] = node
+
+    def contains(self, value):
+        current = self.head
+
+        for level in range(self.level - 1, -1, -1):
+            while (
+                current.next[level] is not None
+                and current.next[level].value < value
+            ):
+                current = current.next[level]
+
+        current = current.next[0]
+
+        return (
+            current is not None
+            and current.value == value
+        )
+
+    def __contains__(self, value):
+        return self.contains(value)
+
+
+
+