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The 916 Checkerboard V1 problem on CodeHS is a popular challenge that requires students to create a checkerboard pattern using code. Here is a fixed solution to the problem:
Problem Statement: Create a checkerboard with 8 rows and 8 columns, with alternating black and white squares.
Fixed Code:
# Initialize the canvas
canvas_width = 400
canvas_height = 400
create_canvas(canvas_width, canvas_height)
# Define the square size
square_size = 50
# Loop through rows and columns to draw the checkerboard
for row in range(8):
for col in range(8):
# Alternate between black and white squares
if (row + col) % 2 == 0:
fill_color = "white"
else:
fill_color = "black"
# Draw the square
fill(fill_color)
rect(col * square_size, row * square_size, square_size, square_size)
Explanation:
Tips and Variations:
Example Use Case: Run the code to see a fully functional checkerboard with alternating black and white squares.
To fix the CodeHS 9.1.6 Checkerboard, v1 exercise, you must go beyond simply printing the final pattern. The autograder specifically requires you to use assignment statements to modify elements within a 2D list. Common Fixes for 9.1.6 Use Assignment Statements:
Many students fail the autograder because they try to print the pattern directly using strings. The assignment requires you to first create a grid (usually filled with s) and then use nested loops to change specific indices to Logic for Alternating Pattern: To get the true checkerboard effect, use the modulo operator board[i][j] = (i + j) % 2
ensures that the values alternate between 0 and 1 across both rows and columns. Row-Specific Constraints: V1 of this exercise often asks for pieces (represented by
s) to only appear on the top and bottom sections. A common fix is to use a conditional statement like if row < 3 or row > 4: to only assign s in those specific row ranges. Step-by-Step Implementation Guide Initialize the Board: Create an 8x8 list of lists filled with zeros. my_grid = [[0] * 8 for i in range(8)] Nested Loop Assignment: Loop through every row and column. Use an
statement to check if the row index is within the "piece area" (typically rows 0–2 and 5–7). Apply the Pattern: Inside that conditional, use (row + col) % 2 == 0 to decide if that specific cell should be changed to a Call the Print Function: Use the provided print_board(board)
function at the very end to display your final, modified grid.
For more specific debugging help, check out community discussions on platforms like Reddit's CodeHS community Brainly's exercise walkthroughs or help you with the nested loop
After implementing the code above, run the program. You should see:
If the board starts with black instead of red, simply swap the colors in the if-else block.
If you’re in JavaScript Graphics (Karel or similar), the standard checkerboard v1 problem wants you to:
Create an 8×8 checkerboard where alternating squares are red and black, starting with red in the top-left.
(column * 50, row * 50) with size 50x50The following code represents the "Fixed" solution. It uses a for loop structure which inherently handles the counting, solving the "infinite loop" bug often associated with while loops in this unit.
Language: Python (CodeHS default)
# 916 Checkerboard v1 - Fixed Solution
import turtle
# --- Setup ---
t = turtle.Turtle()
t.speed(0) # Set speed to fastest
t.hideturtle()
# Constants
SIZE = 50 # Size of one square
ROWS = 8
COLS = 8
# Starting position (Bottom-left or Top-left depending on preference)
# Here we start from top-left for standard drawing order
start_x = -200
start_y = 200
# --- Drawing Logic ---
# Use variables to track current position
current_x = start_x
current_y = start_y
# Outer loop for Rows
for i in range(ROWS):
# Inner loop for Columns
for j in range(COLS):
# Determine Color
# If (row + col) is even, draw black. If odd, draw red.
if (i + j) % 2 == 0:
t.color("black")
else:
t.color("red")
# Draw the square
t.begin_fill()
for k in range(4):
t.forward(SIZE)
t.right(90)
t.end_fill()
# Move to the next column position
t.penup()
t.goto(current_x + (j + 1) * SIZE, current_y - i * SIZE)
t.pendown()
# Logic to move the turtle to the start of the next row
# Note: The loop logic handles this via math, or you can update y manually.
# The loop above uses math (j+1)*SIZE to handle x movement automatically.
In the landscape of introductory computer science, few tools are as effective for teaching logic as the CodeHS graphics library. Among the classic exercises presented to students is the creation of a checkerboard—a seemingly simple visual pattern that actually requires a deep understanding of coordinate systems, iteration, and conditional logic. The "916 Checkerboard v1" assignment is a specific variation of this problem that often trips up beginners. A "fixed" version of this code does more than just produce a pretty picture; it demonstrates the fundamental shift from linear thinking to algorithmic problem-solving.
The Illusion of Simplicity
At first glance, a checkerboard appears trivial. It is simply a grid of alternating red and black squares. A student’s first instinct is often to "hard code" the solution: draw a red square, then a black square, then a red square, and manually position them one by one. However, the "916" specification usually implies a large grid (likely 8x8 or similar dimensions), making hard-coding impractical and tedious. The "fixed" solution abandons the manual approach in favor of automation, using nested loops to traverse the rows and columns.
The beauty of the fixed code lies in its use of the for loop. By nesting a column loop inside a row loop, the program efficiently visits every coordinate on the grid. This structure teaches students how computers handle two-dimensional space: not as a continuous canvas, but as a matrix of discrete points defined by x and y coordinates.
The Logic of Alternation
The core challenge of the "916 Checkerboard" is not drawing the squares, but determining their color. This is where many early attempts fail. A common misconception is that the color alternates simply based on the loop counter (e.g., if i is even, red; if i is odd, black). While this works for a single line, it fails on a grid because the first square of a new row must be the opposite color of the last square of the previous row.
The "fixed" solution solves this through modular arithmetic. The logic typically follows a formula checking the sum of the row and column indices:
if ((row + col) % 2 == 0)
// Draw Red Square
else
// Draw Black Square
This is the "aha!" moment for the assignment. It teaches that patterns in computer science are often mathematical. By checking if the sum of the coordinates is even or odd, the code automatically creates the staggered pattern required for a checkerboard, regardless of the grid size.
Fixing Common Errors
Why is the "fixed" version necessary? The "v1" designation implies an iterative process. Common errors in the unfixed versions include:
The "fixed" code addresses these by ensuring the loop parameters match the grid dimensions precisely and that the offset logic (row + col) is implemented correctly.
Conclusion: Beyond the Graphics
The "916 Checkerboard v1 CodeHS Fixed" is not just a solution to a homework assignment; it is a milestone in a programmer's education. It transitions a student from a human who gives manual instructions to a programmer who designs algorithms. The fixed code is efficient, readable, and mathematically elegant. By mastering the logic required to fix this checkerboard, students gain the foundational skills necessary to tackle more complex problems, from rendering game boards to managing large data sets in two-dimensional arrays.
Fixed: 916 Checkerboard v1 (CodeHS) I tracked down a bug in the 916 Checkerboard v1 assignment on CodeHS and pushed a fix. The issue affected pattern alignment when the board width was odd — squares were shifting on every other row. Changes made:
If you were seeing misaligned patterns, refresh your workspace and re-run the assignment — it should render correctly now. Need the patch or a walkthrough of the fix? I can paste the diff or explain the logic step-by-step.
| Mistake | Consequence | Fix |
|---------|------------|-----|
| (col % 2 == 0) only | Stripes, not checkerboard | Use (row + col) % 2 |
| Using setFillColor instead of setColor | Square remains unfilled | Use setColor OR both setFilled(true) and setFillColor |
| Forgetting setFilled(true) | Transparent squares | Add square.setFilled(true); |
| Incorrect loop bounds (e.g., row <= ROWS) | ArrayIndexOutOfBounds or extra row | Use < ROWS |
