rename Range queries -> range_queries (#646)

range_queries/bit.cpp

@@ -0,0 +1,76 @@
+// Binary Indexed Tree.
+#include<bits/stdc++.h>
+
+using namespace std;
+
+class Bit
+{
+    int n;
+    vector<int> bit;
+    inline int offset(int x)
+    {
+        return (x & (-x));
+    }
+
+    public:
+
+        Bit(vector<int>& arr)
+	{
+            n = arr.size();
+            bit.assign(n + 1, 0);
+            for (int i = 0; i < n; ++i)
+	    {
+                update(i, arr[i]);
+            }
+        }
+    Bit(int x)
+    {
+        n = x;
+        bit.assign(n + 1, 0);
+    }
+
+    void update(int id, int val)
+    {
+        // Add val at id
+        id++;
+        while (id <= n)
+	{
+            bit[id] += val;
+            id += offset(id);
+        }
+    }
+
+    int sum(int id)
+    {
+        // Get prefix sum upto id.
+        id++;
+        int res = 0;
+        while (id > 0)
+	{
+            res += bit[id];
+            id -= offset(id);
+        }
+        return res;
+    }
+
+    int sum_range(int l, int r)
+    {
+        return sum(r) - sum(l - 1);
+    }
+};
+
+int main()
+{
+    int n = 5;
+    vector<int> arr = { 1, 2, 3, 4, 5 };
+    Bit x(arr);
+
+    assert(x.sum_range(0, 0) == 1);
+    assert(x.sum_range(0, 1) == 3);
+    assert(x.sum_range(0, 2) == 6);
+    x.update(0, 6);
+    assert(x.sum_range(0, 0) == 6);
+    assert(x.sum_range(0, 1) == 8);
+    assert(x.sum_range(0, 2) == 11);
+	return 0;
+}