Fix 7.551 tests and solution

It was not consistent with the other "middle" exercises.

Author: SlimTim10

src/exercises/07-arrays-exercises.js

@@ -392,13 +392,15 @@ The following lines should help you see if your function works correctly.
 
 // console.log('middleN tests');
 // console.log(middleN(1, [1, 2, 3, 4, 5]), '=== [3]');
-// console.log(middleN(1, [1, 2, 3, 4, 5, 6]), '=== [4]');
+// console.log(middleN(1, [1, 2, 3, 4, 5, 6]), '=== [3]');
+// console.log(middleN(2, [1, 2, 3, 4, 5]), '=== [2, 3]');
+// console.log(middleN(2, [1, 2, 3, 4, 5, 6]), '=== [2, 3]');
 // console.log(middleN(3, [1, 2, 3]), '=== [1, 2, 3]');
 // console.log(middleN(3, [1, 2, 3, 4, 5]), '=== [2, 3, 4]');
-// console.log(middleN(2, [1, 2, 3, 4, 5]), '=== [3, 4]');
 // console.log(middleN(3, [1, 2, 3, 4, 5, 6, 7]), '=== [3, 4, 5]');
-// console.log(middleN(4, [1, 2, 3, 4, 5, 6, 7, 8, 9]), '=== [4, 5, 6, 7]');
-// console.log(middleN(4, [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]), '=== [4, 5, 6, 7]');
+// console.log(middleN(3, [1, 2, 3, 4, 5, 6, 7, 8]), '=== [3, 4, 5]');
+// console.log(middleN(4, [1, 2, 3, 4, 5, 6, 7, 8, 9]), '=== [3, 4, 5, 6]');
+// console.log(middleN(4, [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]), '=== [3, 4, 5, 6]');
 
 
 // Practice using the sort() method

src/exercises/07-arrays-solutions.js

@@ -549,21 +549,23 @@ const middleN = (n, xs) => {
   const m = middleIndex(xs);
   const half = Math.floor(n / 2);
   if (isEven(n)) {
-    return xs.slice(m - half + 1, m + half + 1);
+    return xs.slice(m - half, m + half);
   } else {
     return xs.slice(m - half, m + half + 1);
   }
 };
 
 console.log('middleN tests');
 console.log(middleN(1, [1, 2, 3, 4, 5]), '=== [3]');
-console.log(middleN(1, [1, 2, 3, 4, 5, 6]), '=== [4]');
+console.log(middleN(1, [1, 2, 3, 4, 5, 6]), '=== [3]');
+console.log(middleN(2, [1, 2, 3, 4, 5]), '=== [2, 3]');
+console.log(middleN(2, [1, 2, 3, 4, 5, 6]), '=== [2, 3]');
 console.log(middleN(3, [1, 2, 3]), '=== [1, 2, 3]');
 console.log(middleN(3, [1, 2, 3, 4, 5]), '=== [2, 3, 4]');
-console.log(middleN(2, [1, 2, 3, 4, 5]), '=== [3, 4]');
 console.log(middleN(3, [1, 2, 3, 4, 5, 6, 7]), '=== [3, 4, 5]');
-console.log(middleN(4, [1, 2, 3, 4, 5, 6, 7, 8, 9]), '=== [4, 5, 6, 7]');
-console.log(middleN(4, [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]), '=== [4, 5, 6, 7]');
+console.log(middleN(3, [1, 2, 3, 4, 5, 6, 7, 8]), '=== [3, 4, 5]');
+console.log(middleN(4, [1, 2, 3, 4, 5, 6, 7, 8, 9]), '=== [3, 4, 5, 6]');
+console.log(middleN(4, [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]), '=== [3, 4, 5, 6]');
 
 
 // Practice using the sort() method