Added segment tree data structure

Author: AlirezaRa94

.gitignore

@@ -1,5 +1,6 @@
 .idea/
 console*.py
 console*.cpp
+*.sql
 __pycache__
 _trial_temp/

data_structures/trees/segment_tree.py

@@ -0,0 +1,41 @@
+"""
+Segment Tree Data Structure
+"""
+
+
+class SegmentTree:
+    def __init__(self, arr):
+        self.n = len(arr)
+        self.tree = [0] * 2 * self.n
+        self.build(arr)
+
+    def size(self):
+        return len(self.tree)
+
+    def build(self, arr):
+        for i in range(self.n):
+            self.tree[self.n + i] = arr[i]
+        for i in range(self.n - 1, 0, -1):
+            self.tree[i] = self.tree[i << 1] + self.tree[i << 1 | 1]
+
+    def update(self, ind, val):
+        ind += self.n
+        diff = val - self.tree[ind]
+        while ind > 0:
+            self.tree[ind] += diff
+            ind >>= 1
+
+    def query(self, left, right):
+        left += self.n
+        right += self.n
+        s = 0
+        while left < right:
+            if left & 1:
+                s += self.tree[left]
+                left += 1
+            if right & 1:
+                right -= 1
+                s += self.tree[right]
+            left >>= 1
+            right >>= 1
+        return s

tests/test_segment_tree.py

@@ -0,0 +1,36 @@
+from typing import Optional, List
+from unittest import TestCase
+
+from data_structures.trees.segment_tree import SegmentTree
+
+
+class TestHeap(TestCase):
+    def setUp(self) -> None:
+        self.segment_tree: Optional[SegmentTree] = None
+        self.sample_data: List = [1, 10, 3, 8, 12, 9, 4, 15, 24]
+
+    def build_sample(self):
+        self.segment_tree = SegmentTree(self.sample_data)
+
+    def test_build(self):
+        self.build_sample()
+        self.assertEqual(self.segment_tree.size(), len(self.sample_data) * 2)
+        self.assertEqual(self.segment_tree.tree[1], sum(self.sample_data))
+
+    def test_update(self):
+        self.build_sample()
+        new_val = 20
+        ind = 2
+        self.segment_tree.update(ind, new_val)
+        tree_ind = ind + len(self.sample_data)
+        self.assertEqual(self.segment_tree.tree[tree_ind], new_val)
+        self.assertEqual(
+            self.segment_tree.tree[1],
+            sum(self.sample_data) + new_val - self.sample_data[ind]
+        )
+
+    def test_query(self):
+        self.build_sample()
+        l, r = 2, 7
+        q = self.segment_tree.query(l, r)
+        self.assertEqual(q, sum(self.sample_data[l:r]))