Added binary indexed tree

Binary_Indexed_Tree.cpp

@@ -0,0 +1,57 @@
+#include <iostream>
+#include <vector>
+
+using namespace std;
+
+class BinaryIndexedTree
+{
+private:
+    vector<int> nums;
+
+public:
+    BinaryIndexedTree(int size)
+    {
+        this->nums.resize(size + 1, 0);
+    }
+    void update(int i, int x)
+    {
+        if (i == 0)
+            return;
+        for (int j = i; j < this->nums.size(); j += (j & -j))
+            this->nums[j] += x;
+    };
+
+    int query(int i)
+    {
+        if (i == 0)
+            return 0;
+        int ans = 0;
+        for (int j = i; j > 0; j -= (j & -j))
+            ans += this->nums[j];
+        return ans;
+    };
+};
+
+int main()
+{
+    int n = 100;
+
+    BinaryIndexedTree *bit = new BinaryIndexedTree(n);
+
+    for (int i = 1; i <= n; i++)
+        bit->update(i, i);
+
+    // Alternate update and query
+    for (int i = 1; i <= n; i++)
+    {
+        if (i % 2 == 0)
+            bit->update(i, i / 2);
+        else
+        {
+            int l = 1, r = n;
+            cout << (bit->query(r) - bit->query(l - 1)) << endl;
+        }
+    }
+
+    return 0;
+}