skip list done

Author: ZabihollahNamazi

Sprint-2/implement_skip_list/skip_list.py

@@ -0,0 +1,53 @@
+import random
+
+class SkipNode:
+    def __init__(self, value, height):
+        self.value = value
+        self.next = [None] * height
+
+class SkipList:
+    def __init__(self, max_height=16):
+        self.max_height = max_height
+
+        self.head = SkipNode(None, self.max_height)
+        self.level = 1 
+
+    def _random_height(self) -> int:
+        height = 1
+        while random.random() < 0.5 and height < self.max_height:
+            height += 1
+        return height
+
+    def insert(self, value) -> None:
+        update = [None] * self.max_height
+        current = self.head
+
+        for i in range(self.max_height - 1, -1, -1):
+            while current.next[i] is not None and current.next[i].value < value:
+                current = current.next[i]
+            update[i] = current
+
+        node_height = self._random_height()
+        new_node = SkipNode(value, node_height)
+
+        for i in range(node_height):
+            new_node.next[i] = update[i].next[i]
+            update[i].next[i] = new_node
+
+    def __contains__(self, value) -> bool:
+        current = self.head
+
+        for i in range(self.max_height - 1, -1, -1):
+            while current.next[i] is not None and current.next[i].value < value:
+                current = current.next[i]
+
+        current = current.next[0]
+        return current is not None and current.value == value
+
+    def to_list(self) -> list:
+        result = []
+        current = self.head.next[0]
+        while current is not None:
+            result.append(current.value)
+            current = current.next[0]
+        return result