Added Fenwick tree aka Binary indexed tree, used for dynamic sum queries.

Author: prince776

DataStructures/RangeQueryDS/binary_indexed_tree.cpp

@@ -0,0 +1,33 @@
+#include <bits/stdc++.h>
+using namespace std;
+
+// BIT[] is 1-based indexed, hence size = n + 1.
+
+const int n = 5;
+
+int BIT[n + 1];
+
+void update(int x, int delta) // add delta at index x
+{	
+	for (; x <= n; x += x &-x)
+		BIT[x] += delta; // update sum value at all indices which cover x
+}
+
+int query(int x)
+{
+	int sum = 0;
+	for (; x > 0; x -= x&-x)
+		sum += BIT[x];
+	return sum;
+}
+
+int main()
+{
+	int a[] = {1, 2, 3, 4, 5};
+	for (int i = 0; i < n; i++)
+	{
+		update(i + 1, a[i]);
+	}
+	cout << "sum i, 1 to 3: " << query(4) - query(1) << "\n";
+	return 0;
+}