Fenwick Tree impl in py (#3)

Signed-off-by: jparisu <[email protected]>

docs/md/intermedio/fenwick/fenwick_cpp.md

@@ -1,10 +1,4 @@
-# Bucles [C++]
-
-```{contents}
-:local:
-:depth: 2
-```
-
+# Fenwick [C++]
 
 ```cpp
 #include <iostream>
@@ -21,11 +15,11 @@ struct FenwickTree {
     {}
 
     // O(logN)
-    // Add value to the element at index (index starts on 0)
-    void update(int index, int value) {
+    // Add delta to the element at index (index starts on 0)
+    void update(int index, int delta) {
         index++;
         while (index <= n) {
-            tree[index - 1] += value;
+            tree[index - 1] += delta;
             index += index & -index;
         }
     }
@@ -54,9 +48,9 @@ struct FenwickTree {
     }
 
     // O(logN)
-    // Return the sum from a to b (both included)
-    int biquery(int a, int b) {
-        return query_includes(b) - query(a);
+    // Return the sum from start to end (both included) (index starts on 0)
+    int query_range(int start, int end) {
+        return query_includes(end) - query(start);
     }
 
     vector<int> tree;

docs/md/intermedio/fenwick/fenwick_py.md

@@ -1,10 +1,43 @@
-# Bucles [Python]
+# Fenwick [Python]
 
-```{contents}
-:local:
-:depth: 2
-```
+```py
+class FenwickTree:
+
+    # O(N)
+    # Create a Fenwick tree with n elements, all initialized to zero
+    def __init__(self, size):
+        self.size = size
+        self.tree = [0] * (size)
+
+    # O(logN)
+    # Add delta to the element at index (index starts on 0)
+    def update(self, index, delta):
+        index += 1
+        while index <= self.size:
+            self.tree[index - 1] += delta
+            index += index & -index
+
+    # O(logN)
+    # Return the sum from 0 to index (no included) (index starts on 0)
+    def query(self, index):
+        acc = 0
+        while index > 0:
+            acc += self.tree[index - 1]
+            index -= index & -index
+        return acc
+
+    # O(logN)
+    # Return the sum from 0 to index (included) (index starts on 0)
+    def query_includes(self, index):
+        acc = 0
+        index += 1
+        while index > 0:
+            acc += self.tree[index - 1]
+            index -= index & -index
+        return acc
 
-```{todo}
-`Work In Progress`
+    # O(logN)
+    # Return the sum from start to end (both included) (index starts on 0)
+    def query_range(self, start, end):
+        return self.query_includes(end) - self.query(start)
 ```