## Homework 1 - Bit

HW 1 is made a range of Bit problems. The whole thing is due Wed Jan 20th at 11:55pm.

LaIR helper hours (linked off course page) begin for the quarter on Mon night.

Solve these problems using loops and logic like the lecture examples (not using Python features like for, range, int counting, break, and, or .. which we have not covered yet.)

Work on your code using one case at a time. As a last step, select the "Run All" option in the menu and Run to check your code against all the cases. If successful, the output is "All Correct" at the top with the big checkmark, which means your code produces the correct output. You should also check your code over for clean style. (We will explain separately how you submit your working code.)

## 1-6 Warmups

These first 6 problems are 1 function each - no extra decomposition.

1. top-rgb

2. top-bot

4. top-logic2

5. top-bluegreen

## 7. Big Red S

Now for some bigger problems made of several functions. For the Big Red S problem, the function decomposition is provided. Use the radio buttons at the top of the page to build and test the functions one at a time to build the whole thing.

Suggestion: the big_red() function itself can be solved with 1 while-loop and 1 if-statement. Consider the point where your code has drawn the first S. Now you need to find the next green square for the next S. You do not need a new while-loop to find the next green square. Let the while loop you already have do it.

7. Big Red

First work on the helper functions which have their own tests, so you can perfect them before going on to Big Red:

Big Red before

Big Red after

## 8. Triple

8. Triple

For this problem, bit starts facing west next to a "rectangle" made of 1 or more blocks. First bit does one "side" move, moving forward while there are blocks to the left, painting squares green. There's a boundary detail here: paint the squares next to a block green, but not the last square.

(Used to do this with colors, now just green. Art here needs to be updated)

Before side move:

After side move:

To complete the rectangle, turn left, move, and do another side move. Then do the last side. That completes one rectangle, which looks like this:

The overall "triple" problem is just 3 rectangles put together, with a right turn making the transition to the 2nd and 3rd rectangles, like this:

After the whole triple:

The main function for this problem is called do_triple() and it solves the whole problem. You should decompose out 2 or more helper functions to help solve the problem. (Nick's solution uses 2 helper functions.) Typically, helper functions are above the main function in the text, but it's not a requirement. For each decomposed helper function write a 1 or 2 sentence description within the """triple quotes""" at the top of the function summarizing what the function does. For the wording of your description, you may assume the reader is familiar with the definitions and terminology of the problem itself. Your description should address the pre and post conditions of the function (and of course you need to have those ideas clear in your head in order to mesh the functions together).

Suggestion: A common source of bugs in this sort of code is accidentally using different pre/post conditions for a function in different parts of the code. Write your pre/post down in the """triple quotes""" so it's really set in your mind.

## 9. Checkerboard

For this problem, bit starts in the upper left corner, facing down. Move bit to the lower left corner, filling in all the rows with a checkerboard pattern, like this:

Before:

After:

It's handy to have terms for the two row types — we'll say the topmost row is "type 0", since the blue squares begin right away, and the second row is "type 1". This is a classic, algorithmic CS106A problem. Make a little diagram to think through each function.

Your code should be able to solve any size world that is 2x2 or larger, and the world may not be square.

The main function for this project is called do_checkerboard() and it solves the whole problem. As with the Triple problem, decompose out 2 or more helper functions to help solve the problem. (Nick's solution uses 2 helper functions.) For each decomposed helper function write a 1 or 2 sentence description within the """triple quotes""" at the top of the function describing what it does as above. A clear definition of bit's position and facing in the pre/post conditions is vital to mesh the functions together.

Here are some friendly suggestions to keep from getting too stuck:

Suggestion 1: There's a non-obvious but extremely cute coding trick that works here. It's so satisfying, and yet beyond imagining, we're just going to tell you: the code that solves the type-1 row can call the code that solves the type-0 row.

Suggestion 2: It's tempting to do a zig-zag pattern, one row going left-to-right, and the next row going right-to-left — that's how you would do it as a person walking around. Do not do it that way! Unfortunately, that zig-zag scheme works poorly as an algorithm because of the pre/post conditions. With the zig-zag scheme, type-0 and type-1 rows have different pre/post conditions, facing opposite directions, so it's nearly impossible to mesh them together. It works more cleanly to do all the rows in the same direction, like the lecture examples, so their pre/post conditions are uniform, all going the same direction.