implement skip list

Author: ebrahimbeiati

Sprint-2/implement_skip_list/skip_list.py

@@ -0,0 +1,72 @@
+import random
+
+
+class Node:
+    def __init__(self, height, value):
+        self.value = value
+        self.forward = [None] * height
+
+
+class SkipList:
+    MAX_HEIGHT = 16
+    P = 0.5
+
+    def __init__(self):
+        self.head = Node(self.MAX_HEIGHT, None)
+        self.level = 1
+        self.length = 0
+
+    def __len__(self):
+        return self.length
+
+    def random_height(self):
+        height = 1
+        while random.random() < self.P and height < self.MAX_HEIGHT:
+            height += 1
+        return height
+
+    def _find_updated_path(self, value):
+        update = [None] * self.MAX_HEIGHT
+        current = self.head
+        for i in range(self.level - 1, -1, -1):
+            while current.forward[i] and current.forward[i].value < value:
+                current = current.forward[i]
+            update[i] = current
+        return update
+
+    def __contains__(self, value):
+        current = self.head
+
+        for i in range(self.level - 1, -1, -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 insert(self, value):
+        update = self._find_updated_path(value)
+        forward_node = update[0].forward[0]
+
+        if forward_node and forward_node.value == value:
+            return
+        node_height = self.random_height()
+        if node_height > self.level:
+            for i in range(self.level, node_height):
+                update[i] = self.head
+            self.level = node_height
+
+        new_node = Node(node_height, value)
+
+        for i in range(node_height):
+            new_node.forward[i] = update[i].forward[i]
+            update[i].forward[i] = new_node
+        self.length += 1
+
+    def to_list(self):
+        result = []
+        current = self.head.forward[0]
+        while current:
+            result.append(current.value)
+            current = current.forward[0]
+        return result