From 5269330e748237c2a7992e95e3655bb74421b2fb Mon Sep 17 00:00:00 2001
From: Gabriel Duarte <gabriellagoa10@yahoo.com.br>
Date: Sun, 8 Nov 2015 23:19:15 -0200
Subject: [PATCH 1/2] Add Fenwick Tree algorithm - Gabriel123Duarte

---
 include/fenwick_tree.h    | 44 +++++++++++++++++++++++++++++++++++++++
 src/fenwick_tree_demo.cpp | 16 ++++++++++++++
 2 files changed, 60 insertions(+)
 create mode 100644 include/fenwick_tree.h
 create mode 100644 src/fenwick_tree_demo.cpp

diff --git a/include/fenwick_tree.h b/include/fenwick_tree.h
new file mode 100644
index 00000000..ba3f581c
--- /dev/null
+++ b/include/fenwick_tree.h
@@ -0,0 +1,44 @@
+#ifndef __FENWICK_H__
+#define __FENWICK_H__
+
+#include <vector>
+
+#define LSONE(x) (x & (-x))
+
+class Fenwick
+{
+	private:
+		std::vector<int> fen;
+	public:
+		Fenwick() {}
+
+		// We don't use the index 0
+		Fenwick(int n)
+		{
+			fen.assign(n + 1, 0);
+		}
+
+		// RSQ 1..a
+		int rsq(int a)
+		{
+			int ans = 0;
+			for(; a; a -= LSONE(a))
+				ans += fen[a];
+			return ans;
+		}
+
+		// RSQ a..b
+		inline int rsq(int a, int b)
+		{
+			return rsq(b) - (a == 1 ? 0 : rsq(a - 1));
+		}
+
+		// Update the value of the k-th element by x
+		void update(int k, int x)
+		{
+			for(; k < (int)fen.size(); k += LSONE(k))
+				fen[k] += x;	
+		}
+};
+
+#endif
\ No newline at end of file
diff --git a/src/fenwick_tree_demo.cpp b/src/fenwick_tree_demo.cpp
new file mode 100644
index 00000000..d5e294de
--- /dev/null
+++ b/src/fenwick_tree_demo.cpp
@@ -0,0 +1,16 @@
+#include <cstdio>
+#include "fenwick_tree.h"
+
+int main()
+{
+	Fenwick ft(5);
+
+	ft.update(2, 1);
+	ft.update(4, 10);
+
+	printf("%d\n", ft.rsq(1));
+
+	ft.update(1, 5);	
+	printf("%d\n", ft.rsq(1));
+	return 0;
+}
\ No newline at end of file

From 99defa0c2139648cc551509bf583457137598da5 Mon Sep 17 00:00:00 2001
From: Gabriel Duarte <gabriellagoa10@yahoo.com.br>
Date: Mon, 9 Nov 2015 08:53:33 -0200
Subject: [PATCH 2/2] Added some comments in the header file

---
 include/.goutputstream-UUQE8X | 61 +++++++++++++++++++++++++++++++++++
 include/fenwick_tree.h        | 23 +++++++++++--
 2 files changed, 81 insertions(+), 3 deletions(-)
 create mode 100644 include/.goutputstream-UUQE8X

diff --git a/include/.goutputstream-UUQE8X b/include/.goutputstream-UUQE8X
new file mode 100644
index 00000000..e92d1ab5
--- /dev/null
+++ b/include/.goutputstream-UUQE8X
@@ -0,0 +1,61 @@
+/*******************************************************************************
+ * Fenwick Tree
+ *
+ * Data structure providing prefix sums and modify the table in O(log n) - n is the size o the table.
+ *
+ * In this algorithm we use two functions:
+ * - RSQ - This function calculates the range sum query in O(log n)
+ * - Update - This function adjusts the values in the given range in O(log n)
+ *
+ * https://en.wikipedia.org/wiki/Fenwick_tree
+ * 
+ * @author Gabriel Duarte (gabriellagoa10@yahoo.com.br)
+ * @github Gabriel123Duarte
+ *
+ ******************************************************************************/
+
+#ifndef __FENWICK_H__
+#define __FENWICK_H__
+
+#include <vector>
+
+#define LSONE(x) (x & (-x))
+
+class Fenwick
+{
+	private:
+		// Vector representing the table
+		std::vector<int> fen;
+	public:
+		Fenwick() {}
+
+		// We don't use the index 0, because it is the base case
+		Fenwick(int n)
+		{
+			fen.assign(n + 1, 0);
+		}
+
+		// Calculate the 
+		int rsq(int a)
+		{
+			int ans = 0;
+			for(; a; a -= LSONE(a))
+				ans += fen[a];
+			return ans;
+		}
+
+		// RSQ a..b
+		inline int rsq(int a, int b)
+		{
+			return rsq(b) - (a == 1 ? 0 : rsq(a - 1));
+		}
+
+		// Update the value of the k-th element by x
+		void update(int k, int x)
+		{
+			for(; k < (int)fen.size(); k += LSONE(k))
+				fen[k] += x;	
+		}
+};
+
+#endif
diff --git a/include/fenwick_tree.h b/include/fenwick_tree.h
index ba3f581c..e92d1ab5 100644
--- a/include/fenwick_tree.h
+++ b/include/fenwick_tree.h
@@ -1,3 +1,19 @@
+/*******************************************************************************
+ * Fenwick Tree
+ *
+ * Data structure providing prefix sums and modify the table in O(log n) - n is the size o the table.
+ *
+ * In this algorithm we use two functions:
+ * - RSQ - This function calculates the range sum query in O(log n)
+ * - Update - This function adjusts the values in the given range in O(log n)
+ *
+ * https://en.wikipedia.org/wiki/Fenwick_tree
+ * 
+ * @author Gabriel Duarte (gabriellagoa10@yahoo.com.br)
+ * @github Gabriel123Duarte
+ *
+ ******************************************************************************/
+
 #ifndef __FENWICK_H__
 #define __FENWICK_H__
 
@@ -8,17 +24,18 @@
 class Fenwick
 {
 	private:
+		// Vector representing the table
 		std::vector<int> fen;
 	public:
 		Fenwick() {}
 
-		// We don't use the index 0
+		// We don't use the index 0, because it is the base case
 		Fenwick(int n)
 		{
 			fen.assign(n + 1, 0);
 		}
 
-		// RSQ 1..a
+		// Calculate the 
 		int rsq(int a)
 		{
 			int ans = 0;
@@ -41,4 +58,4 @@ class Fenwick
 		}
 };
 
-#endif
\ No newline at end of file
+#endif