Update persistent_segment_tree.py

data_structures/persistent_segment_tree.py

@@ -34,6 +34,19 @@ class PersistentSegmentTree:
         return node
 
     def update(self, version: int, index: int, value: int) -> int:
+        """
+        Updates the value at the given index and returns the new version.
+
+        >>> pst = PersistentSegmentTree([1, 2, 3, 4])
+        >>> version_1 = pst.update(0, 1, 5)  # Update index 1 to 5
+        >>> pst.query(version_1, 0, 3)  # Query sum of all elements in new version
+        13
+        >>> pst.query(0, 0, 3)  # Original version remains unchanged
+        10
+        >>> version_2 = pst.update(version_1, 3, 6)  # Update index 3 to 6 in version_1
+        >>> pst.query(version_2, 0, 3)  # Query sum of all elements in newest version
+        15
+        """
         new_root = self._update(self.roots[version], 0, self.n - 1, index, value)
         self.roots.append(new_root)
         return len(self.roots) - 1
@@ -72,6 +85,20 @@ class PersistentSegmentTree:
         return new_node
 
     def query(self, version: int, left: int, right: int) -> int:
+        """
+        Queries the sum in the given range for the specified version.
+
+        >>> pst = PersistentSegmentTree([1, 2, 3, 4])
+        >>> pst.query(0, 0, 3)  # Sum of all elements in original version
+        10
+        >>> pst.query(0, 1, 2)  # Sum of elements at index 1 and 2 in original version
+        5
+        >>> version_1 = pst.update(0, 1, 5)  # Update index 1 to 5
+        >>> pst.query(version_1, 0, 3)  # Sum of all elements in new version
+        13
+        >>> pst.query(version_1, 1, 2)  # Sum of elements at index 1 and 2 in new version
+        8
+        """
         return self._query(self.roots[version], 0, self.n - 1, left, right)
 
     def _query(self, node: Node, start: int, end: int, left: int, right: int) -> int:
@@ -92,15 +119,13 @@ class PersistentSegmentTree:
         if left <= start and right >= end:
             return node.value
         mid = (start + end) // 2
-        return self._query(node.left, start, mid, left, right) + self._query(
+        return (self._query(node.left, start, mid, left, right) +
-            node.right, mid + 1, end, left, right
+                self._query(node.right, mid + 1, end, left, right))
-        )
 
 
 # Running the doctests
 if __name__ == "__main__":
     import doctest
-
     print("Running doctests...")
     result = doctest.testmod()
     print(f"Ran {result.attempted} tests, {result.failed} failed.")