From 71779c52d7ea38f2b156ac1d5b0907b59a36d5c8 Mon Sep 17 00:00:00 2001
From: alexpantyukhin <apantykhin@gmail.com>
Date: Fri, 4 Nov 2022 00:43:58 +0400
Subject: [PATCH 1/3] add prefix sum

---
 data_structures/arrays/prefix_sum.py | 77 ++++++++++++++++++++++++++++
 1 file changed, 77 insertions(+)
 create mode 100644 data_structures/arrays/prefix_sum.py

diff --git a/data_structures/arrays/prefix_sum.py b/data_structures/arrays/prefix_sum.py
new file mode 100644
index 000000000000..b7553355ac81
--- /dev/null
+++ b/data_structures/arrays/prefix_sum.py
@@ -0,0 +1,77 @@
+"""
+Author  : Alexander Pantyukhin
+Date    : November 3, 2022
+
+Implement the class of prefix sum with useful functions based on it.
+
+"""
+
+class PrefixSum:
+    def __init__(self, array: list[int]) -> None:
+        len_array = len(array)
+        self.prefix_sum = [0] * len_array
+
+        if len_array > 0:
+            self.prefix_sum[0] = array[0]
+
+        for i in range(1, len_array):
+            self.prefix_sum[i] = self.prefix_sum[i - 1] + array[i]
+        
+    def get_sum(self, start: int, end: int) -> int:
+        """
+        The function returns the sum of array from the start to the end indexes.
+        Runtime : O(1)
+        Space: O(1)
+
+        >>> PrefixSum([1,2,3]).get_sum(0, 2)
+        6
+        >>> PrefixSum([1,2,3]).get_sum(1, 2)
+        5
+        >>> PrefixSum([1,2,3]).get_sum(2, 2)
+        3
+        >>> PrefixSum([1,2,3]).get_sum(2, 3)
+        Traceback (most recent call last):
+        ...
+        IndexError: list index out of range
+        """
+        if start == 0:
+            return self.prefix_sum[end]
+
+        return self.prefix_sum[end] - self.prefix_sum[start - 1]
+
+    def contains_sum(self, target_sum: int) -> bool:
+        """
+        The function returns True if array contains the target_sum,
+        False otherwise.
+
+        Runtime : O(n)
+        Space: O(n)
+
+        >>> PrefixSum([1,2,3]).contains_sum(6)
+        True
+        >>> PrefixSum([1,2,3]).contains_sum(5)
+        True
+        >>> PrefixSum([1,2,3]).contains_sum(3)
+        True
+        >>> PrefixSum([1,2,3]).contains_sum(4)
+        False
+        >>> PrefixSum([1,2,3]).contains_sum(7)
+        False
+        >>> PrefixSum([1,-2,3]).contains_sum(2)
+        True
+        """
+
+        sums = set([0])
+        for sum_item in self.prefix_sum:
+            if sum_item - target_sum in sums:
+                return True
+
+            sums.add(sum_item)
+
+        return False
+
+
+if __name__ == "__main__":
+    import doctest
+
+    doctest.testmod()

From 009d6813e1d73060fa91f663b6b3e17e9de5c4c4 Mon Sep 17 00:00:00 2001
From: github-actions <${GITHUB_ACTOR}@users.noreply.github.com>
Date: Thu, 3 Nov 2022 20:45:25 +0000
Subject: [PATCH 2/3] updating DIRECTORY.md

---
 DIRECTORY.md | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/DIRECTORY.md b/DIRECTORY.md
index a2112bcfb7b4..76c7f9dea4e3 100644
--- a/DIRECTORY.md
+++ b/DIRECTORY.md
@@ -162,6 +162,7 @@
 ## Data Structures
   * Arrays
     * [Permutations](data_structures/arrays/permutations.py)
+    * [Prefix Sum](data_structures/arrays/prefix_sum.py)
   * Binary Tree
     * [Avl Tree](data_structures/binary_tree/avl_tree.py)
     * [Basic Binary Tree](data_structures/binary_tree/basic_binary_tree.py)
@@ -174,6 +175,7 @@
     * [Diff Views Of Binary Tree](data_structures/binary_tree/diff_views_of_binary_tree.py)
     * [Fenwick Tree](data_structures/binary_tree/fenwick_tree.py)
     * [Inorder Tree Traversal 2022](data_structures/binary_tree/inorder_tree_traversal_2022.py)
+    * [Is Bst](data_structures/binary_tree/is_bst.py)
     * [Lazy Segment Tree](data_structures/binary_tree/lazy_segment_tree.py)
     * [Lowest Common Ancestor](data_structures/binary_tree/lowest_common_ancestor.py)
     * [Maximum Fenwick Tree](data_structures/binary_tree/maximum_fenwick_tree.py)

From 30aa9431f76ed6db8e6a5d15b5f1510ad3c658e0 Mon Sep 17 00:00:00 2001
From: "pre-commit-ci[bot]"
 <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Date: Thu, 3 Nov 2022 20:47:37 +0000
Subject: [PATCH 3/3] [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci
---
 data_structures/arrays/prefix_sum.py | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/data_structures/arrays/prefix_sum.py b/data_structures/arrays/prefix_sum.py
index b7553355ac81..2243a5308937 100644
--- a/data_structures/arrays/prefix_sum.py
+++ b/data_structures/arrays/prefix_sum.py
@@ -6,6 +6,7 @@
 
 """
 
+
 class PrefixSum:
     def __init__(self, array: list[int]) -> None:
         len_array = len(array)
@@ -16,7 +17,7 @@ def __init__(self, array: list[int]) -> None:
 
         for i in range(1, len_array):
             self.prefix_sum[i] = self.prefix_sum[i - 1] + array[i]
-        
+
     def get_sum(self, start: int, end: int) -> int:
         """
         The function returns the sum of array from the start to the end indexes.
@@ -61,7 +62,7 @@ def contains_sum(self, target_sum: int) -> bool:
         True
         """
 
-        sums = set([0])
+        sums = {0}
         for sum_item in self.prefix_sum:
             if sum_item - target_sum in sums:
                 return True