# Unit 4A - More Code Practice with Arrays

Each coding exercise has its own folder. Open its `.java` file and press **Run** to try it. **Run Tests** checks every graded exercise in this lesson at once.

## Exercise 1

Create a method `sum13(nums)` that takes an array of integers, `nums` and returns the sum of the numbers in the array. However, the number 13 is very unlucky, so do not add it or the number that comes immediately after a 13 to the sum. Return `0` if `nums` is an empty array.

| Example Input | Expected Output |
| --- | --- |
| `sum13({13, 1, 2})` | `2` |
| `sum13({1,13})` | `1` |
| `sum13({4, 13, 8})` | `4` |
| `sum13({13, 1, 13, 3, 2})` | `2` |
| `sum13({})` | `0` |

> Open the `01-sum13-written` folder and edit `Sum13.java`. Press **Run** to try it; **Run Tests** checks it (2 tests).

## Exercise 2

Create a method `has22(nums)` that takes an array of integers, `nums` and returns `true` if there are at least two items in the list that are adjacent and both equal to `2`, otherwise return `false`.

| Example Input | Expected Output |
| --- | --- |
| `has22({1, 2, 2})` | `true` |
| `has22({2, 1, 2})` | `false` |
| `has22({2, 2, 8})` | `true` |
| `has22({3, 3, 5})` | `false` |

> Open the `02-has22-written2` folder and edit `Has22.java`. Press **Run** to try it; **Run Tests** checks it (2 tests).

## Exercise 3

Create the `total89(nums)` method below that takes an array of integers, `nums`, and returns the total of the numbers in `nums` except for all numbers in the array between an 8 and a 9 (inclusive).

| Example Input | Expected Output |
| --- | --- |
| `total89({1, 2})` | `3` |
| `total89({2, 8, 3, 9, 2})` | `4` |
| `total89({8, 3, 5, 9, 6})` | `6` |

> Open the `03-total89-written` folder and edit `Total89.java`. Press **Run** to try it; **Run Tests** checks it (2 tests).

## Exercise 4

Create a method `twoSum(nums, target)` that takes an array of integers `nums` and an integer `target` and returns an array with the indices of two numbers such that they add up to `target`. If no two numbers add up to `target`, it returns an empty array. Assume that each input has exactly one solution, and you may not use the same element twice.

| Example Input | Expected Output |
| --- | --- |
| `twoSum({2,7,11,15}, 9)` | `{0, 1}` |
| `twoSum({2,7,11,15}, 13)` | `{0, 2}` |
| `twoSum({2,7,11,15}, 5)` | `{}` |

> Open the `04-twoSum-written` folder and edit `TwoSum.java`. Press **Run** to try it; **Run Tests** checks it (2 tests).