Added comments to treap

Author: Flygrounder

data_structures/binary tree/treap.py

@@ -3,6 +3,10 @@
 
 
 class Node:
+    """
+    Treap's node
+    Treap is a binary tree by key and heap by priority
+    """
     def __init__(self, key: int):
         self.key = key
         self.prior = random()
@@ -11,28 +15,64 @@ def __init__(self, key: int):
 
 
 def split(root: Node, key: int) -> Tuple[Node, Node]:
-    if root is None:
+    """
+    We split current tree into 2 trees with key:
+
+    Left tree contains all keys less than split key.
+    Right tree contains all keys greater or equal, than split key
+    """
+    if root is None:  # None tree is split into 2 Nones
         return (None, None)
     if root.key >= key:
+        """
+        Right tree's root will be current node.
+        Now we split(with the same key) current node's left son
+        Left tree: left part of that split
+        Right tree's left son: right part of that split
+        """
         l, root.l = split(root.l, key)
         return (l, root)
     else:
+        """
+        Just symmetric to previous case
+        """
         root.r, r = split(root.r, key)
         return (root, r)
 
 
 def merge(left: Node, right: Node) -> Node:
+    """
+    We merge 2 trees into one.
+    Note: all left tree's keys must be less than all right tree's
+    """
     if (not left) or (not right):
+        """
+        If one node is None, return the other
+        """
         return left or right
     if left.key > right.key:
+        """
+        Left will be root because it has more priority
+        Now we need to merge left's right son and right tree
+        """
         left.r = merge(left.r, right)
         return left
     else:
+        """
+        Symmetric as well
+        """
         right.l = merge(left, right.l)
         return right
 
 
 def insert(root: Node, key: int) -> Node:
+    """
+    Insert element
+
+    Split current tree with a key into l, r,
+    Insert new node into the middle
+    Merge l, node, r into root
+    """
     node = Node(key)
     l, r = split(root, key)
     root = merge(l, node)
@@ -41,12 +81,22 @@ def insert(root: Node, key: int) -> Node:
 
 
 def erase(root: Node, key: int) -> Node:
+    """
+    Erase element
+
+    Split all nodes with keys less into l,
+    Split all nodes with keys greater into r.
+    Merge l, r
+    """
     l, r = split(root, key)
     _, r = split(r, key + 1)
     return merge(l, r)
 
 
 def node_print(root: Node):
+    """
+    Just recursive print of a tree
+    """
     if not root:
         return
     node_print(root.l)
@@ -55,6 +105,13 @@ def node_print(root: Node):
 
 
 def interactTreap():
+    """
+    Commands:
+    + key to add key into treap
+    - key to erase all nodes with key
+
+    After each command, program prints treap
+    """
     root = None
     while True:
         cmd = input().split()