         
         lowestAndHighest.append(lowest) // append at index 0
         lowestAndHighest.insert(highest, atIndex: lowestAndHighest.endIndex) // append at index 1
-        
+    }
     return lowestAndHighest
 }
 findMinAndMax([5, 3, 7, 9, 21, 2])

        for j in arr2 {
            if i == j {
                doubles.append(i)
            }
        }
        return doubles
    }
containCommonItems([1, 2, 3, 4, 5], arr2: [6, 7, 8, 9, 10]) // O(n^2)



// check array for missing number in consecutive numbers, return that number (to reuse numbers)

// assign that number to a customer









// take in string, return letter that appears the most frequently

}

isUnique("hello")




