feat(book/arrays): add exercises

Author: amejiarosario

book/content/part02/array.asc

@@ -7,7 +7,7 @@ endif::[]
 === Array
 (((Array)))
 (((Data Structures, Linear, Array)))
-Arrays are one of the most used data structures. You probably have used it a lot but are you aware of the runtimes of  `splice`, `shift`, `indexOf`  and other operations? In this chapter, we are going deeper into the most common operations and their runtimes.
+Arrays are one of the most used data structures. You probably have used it a lot but are you aware of the runtimes of `splice`, `shift`, `indexOf`  and other operations? In this chapter, we are going deeper into the most common operations and their runtimes.
 
 ==== Array  Basics
 
@@ -274,3 +274,47 @@ To sum up, the time complexity of an array is:
 | splice ^| O(n) | Insert and remove from anywhere.
 |===
 //end::table
+
+==== Array Exercises
+
+1. Implement an efficient algorithm that rotate an array `a` an `k` number of times.
+
+[source, javascript]
+----
+/**
+ * Rotate an array left by k number of times.
+ *
+ * @example
+ *    rotateLeft([1,2,3], 1); // [2,3,1]
+ *    rotateLeft([1,2,3,4,5], 4); // [5,1,2,3,4]
+ *
+ *    rotateLeft(Array(1e6).fill(1), 1e4); // 
+ *
+ * @param a - The array
+ * @param k - The number of times the array is rotated
+ */
+function rotateLeft(a, k) {
+  // write you code and test with examples
+}
+----
+
+
+2. Implement an algorithm that takes two arrays of numbers and return a new array with the sum.
+
+[source, javascript]
+----
+/**
+ * Return the sum of two arrays as a new array.
+ *
+ * @example
+ *    sum([1,2,3], [1,1,1]); // [2,3,4]
+ *    sum([1], [9,9,9]); // [1,0,0,0]
+ *
+ * @param {number[]} a - Array of numbers.
+ * @param {number[]} b - Array of numbers.
+ * @returns {number[]} the sum array.
+ */
+function sum(a, b) {
+  // write you code and test with examples
+}
+----