From d68d0ef05c024cb90f96b379c1206b3487847cbc Mon Sep 17 00:00:00 2001
From: Sarot Busala <sabuza97@gmail.com>
Date: Fri, 20 Oct 2017 16:45:17 +0700
Subject: [PATCH] Add Fenwick Tree

Add Fenwick Tree (Binary Index Tree)
---
 data_structures/Binary Tree/FenwickTree.py | 28 ++++++++++++++++++++++
 1 file changed, 28 insertions(+)
 create mode 100644 data_structures/Binary Tree/FenwickTree.py

diff --git a/data_structures/Binary Tree/FenwickTree.py b/data_structures/Binary Tree/FenwickTree.py
new file mode 100644
index 000000000..02e2d6151
--- /dev/null
+++ b/data_structures/Binary Tree/FenwickTree.py	
@@ -0,0 +1,28 @@
+class FenwickTree:
+
+    def __init__(self, SIZE): # create fenwick tree with size SIZE
+        self.Size = SIZE
+        self.ft = [0 for i in range (0,SIZE)]
+
+    def update(self, i, val): # update data (adding) in index i in O(lg N)
+        while (i < self.Size):
+            self.ft[i] += val
+            i += i & (-i)
+
+    def query(self, i): # query cumulative data from index 0 to i in O(lg N)
+        ret = 0
+        while (i > 0):
+            ret += self.ft[i]
+            i -= i & (-i)
+        return ret
+            
+if __name__ == '__main__':
+    f = FenwickTree(100)
+    f.update(1,20)
+    f.update(4,4)
+    print (f.query(1))
+    print (f.query(3))
+    print (f.query(4))
+    f.update(2,-5)
+    print (f.query(1))
+    print (f.query(3))