grains: fix approaches full code example (#2181)

Author: ErikSchierboom

exercises/practice/grains/.approaches/bit-shifting/content.md

@@ -2,7 +2,7 @@
 
 ```csharp
 using System;
-using System.Numerics; // for use with BigInteger
+using System.Numerics; // Allows using BigInteger
 
 public static class Grains
 {
@@ -27,19 +27,20 @@ Instead of using math to calculate the number of grains on a square, you can sim
 To understand how this works, consider just two squares that are represented in binary bits as `00`.
 
 You use the [left-shift operator][left-shift-operator] to set `1` at the position needed to make the correct decimal value.
+
 - To set the one grain on Square One you shift `1` for `0` positions to the left.
-So, if `n` is `1` for square One, you subtract `n` by `1` to get `0`, which will not move it any positions to the left.
-The result is binary `01`, which is decimal `1`.
+  So, if `n` is `1` for square One, you subtract `n` by `1` to get `0`, which will not move it any positions to the left.
+  The result is binary `01`, which is decimal `1`.
 - To set the two grains on Square Two you shift `1` for `1` position to the left.
-So, if `n` is `2` for square Two, you subtract `n` by `1` to get `1`, which will move it `1` position to the left.
-The result is binary `10`, which is decimal `2`.
+  So, if `n` is `2` for square Two, you subtract `n` by `1` to get `1`, which will move it `1` position to the left.
+  The result is binary `10`, which is decimal `2`.
 
-| Square  | Shift Left By | Binary Value | Decimal Value |
-| ------- | ------------- | ------------ | ------------- |
-|       1 |             0 |         0001 |             1 |
-|       2 |             1 |         0010 |             2 |
-|       3 |             2 |         0100 |             4 |
-|       4 |             3 |         1000 |             8 |
+| Square | Shift Left By | Binary Value | Decimal Value |
+| ------ | ------------- | ------------ | ------------- |
+| 1      | 0             | 0001         | 1             |
+| 2      | 1             | 0010         | 2             |
+| 3      | 2             | 0100         | 4             |
+| 4      | 3             | 1000         | 8             |
 
 For `Total` we want all of the 64 bits set to `1` to get the sum of grains on all sixty-four squares.
 The easy way to do this is to set the 65th bit to `1` and then subtract `1`.
@@ -48,14 +49,14 @@ To go back to our two-square example, if we can grow to three squares, then we c
 which is decimal `4`.
 By subtracting `1` we get `3`, which is the total amount of grains on the two squares.
 
-| Square  | Binary Value | Decimal Value |
-| ------- | ------------ | ------------- |
-|       3 |         0100 |             4 |
+| Square | Binary Value | Decimal Value |
+| ------ | ------------ | ------------- |
+| 3      | 0100         | 4             |
 
-| Square  | Sum Binary Value | Sum Decimal Value |
-| ------- | ---------------- | ----------------- |
-|       1 |             0001 |                 1 |
-|       2 |             0011 |                 3 |
+| Square | Sum Binary Value | Sum Decimal Value |
+| ------ | ---------------- | ----------------- |
+| 1      | 0001             | 1                 |
+| 2      | 0011             | 3                 |
 
 ## Shortening
 

exercises/practice/grains/.approaches/max-value/content.md

@@ -1,9 +1,22 @@
-# `System.UInt64.MaxValue` for Total
+# `Int64.MaxValue` for Total
 
 ```csharp
-public static ulong Total()
+using System;
+
+public static class Grains
 {
-  return System.UInt64.MaxValue;
+    public static double Square(int i)
+    {
+        if (i is <= 0 or > 64)
+            throw new ArgumentOutOfRangeException(nameof(i));
+
+        return Math.Pow(2, i - 1);
+    }
+
+    public static double Total()
+    {
+        return UInt64.MaxValue;
+    }
 }
 ```
 

exercises/practice/grains/.approaches/pow/content.md

@@ -2,6 +2,7 @@
 
 ```csharp
 using System;
+using System.Linq;
 
 public static class Grains
 {