Mastering CodeHS 9.1.6: Checkerboard, v1 In the CodeHS "Introduction to Computer Science in Python 3" curriculum, exercise 9.1.6: Checkerboard, v1 introduces students to representing complex grids using
. This specific version focuses on the foundational step of creating a 2D structure where values represent different game states: for a checker piece and for an empty square. The Assignment Objective The goal is to create an
grid stored as a list of lists. Unlike a fully alternating board, version 1 requires a simplified pattern where: top three rows contain alternating pieces ( middle two rows are completely empty (all bottom three rows contain alternating pieces ( Step-by-Step Implementation 1. Initialize the 2D Grid First, create an empty list called
. Use a loop to populate it with 8 rows, each initially filled with zeros to establish the basic structure. 2. Target Specific Rows for Pieces
To match the checkerboard layout, you must use nested loops to iterate through the grid. Use a conditional statement to identify rows (top) and rows 3. Assign Alternating Values
Within those specific rows, use modular arithmetic—specifically (row + column) % 2 —to decide if a cell should be a
. This ensures that adjacent cells never have the same value, creating the classic checkerboard look. 4. Print the Result Finally, pass your populated list to the provided print_board function to visualize the grid in the console. Example Solution Code
The following structure is commonly used to pass the CodeHS autograder, which requires actual assignment statements (e.g., board[i][j] = 1 ) rather than just printing the expected output. # Function to print the board provided by CodeHS print_board range(len(board)): print( .join([str(x) board[i]])) # 1. Initialize an 8x8 grid with all 0s ): board.append([ # 2. Use nested loops to place checker pieces (1s) # Top 3 rows and Bottom 3 rows # Alternating pattern: 1 if (row + col) is even (row + col) % : board[row][col] = # 3. Display the board print_board(board) Use code with caution. Copied to clipboard Common Pitfalls Static Printing: Simply printing the pattern using print("0 1 0 1...")
will fail the autograder. You must actually modify the list elements. Indexing Errors: Remember that Python indices start at grid has indices ranging from Middle Rows: Ensure rows
remain all zeros, as these represent the empty "no-man's land" in the middle of a checkers game. 9.1.6 checkerboard v1 codehs
For further help with 2D lists, check out official resources like the CodeHS Python 3 Course Explore Page or community discussions on Reddit's r/codehs Checkerboard v2
, which introduces different values for red and black pieces?
The solution to CodeHS 9.1.6: Checkerboard, v1 involves creating an 8x8 grid of zeros and then using nested loops to modify the values in specific rows to represent checker pieces. Logic Breakdown
Initialize the Grid: Create a 2D list (an 8x8 grid) filled entirely with 0s.
Target Specific Rows: The "v1" version of this exercise typically requires placing pieces (represented by 1s) in the top three rows and the bottom three rows.
Assign Values: Within nested loops, check if the current row index is part of the top three (indices 0–2) or bottom three (indices 5–7). If so, change the 0 to a 1 using an assignment statement like board[i][j] = 1. Step-by-Step Implementation
Create the initial 8x8 gridUse a loop to append lists of eight zeros to an empty master list. board = [] for i in range(8): board.append([0] * 8) Use code with caution. Copied to clipboard
Use nested loops to update piece positionsIterate through every row and column. Use an if statement to identify the top three and bottom three rows.
for i in range(8): for j in range(8): # Check if row is in the top 3 or bottom 3 if i < 3 or i > 4: board[i][j] = 1 Use code with caution. Copied to clipboard Mastering CodeHS 9
Print the resulting boardCall the provided print_board(board) function to display the grid as formatted text. ✅ Final Result The final code should look similar to this:
def print_board(board): for row in board: print(" ".join([str(x) for x in row])) # 1. Create an 8x8 board of 0s board = [] for i in range(8): board.append([0] * 8) # 2. Assign 1s to the top 3 and bottom 3 rows for i in range(8): for j in range(8): if i < 3 or i > 4: board[i][j] = 1 # 3. Output the result print_board(board) Use code with caution. Copied to clipboard
The program successfully initializes a grid and uses assignment statements to modify specific elements, fulfilling the autograder's requirements.
In the CodeHS exercise 9.1.6: Checkerboard v1, the goal is to create a checkerboard pattern using a 2D array. This specific version usually focuses on populating the grid with alternating values (like 0 and 1) to represent the two different colors of a board. Logic Breakdown
The key to identifying a "checkerboard" pattern is the relationship between the row index ( ) and the column index ( A cell belongs to one "color" if the sum of its indices ( ) is even.
It belongs to the other "color" if the sum of its indices is odd. Example Code Implementation (Java)
Here is a solid implementation using nested loops to initialize the 2D array:
public class Checkerboard extends ConsoleProgram public static void main(String[] args) int size = 8; int[][] board = new int[size][size]; for (int row = 0; row < size; row++) for (int col = 0; col < size; col++) // Check if the sum of row and col is even if ((row + col) % 2 == 0) board[row][col] = 1; // "Color A" else board[row][col] = 0; // "Color B" // Helper method to print the board printBoard(board); private static void printBoard(int[][] board) for (int[] row : board) for (int val : row) System.out.print(val + " "); System.out.println(); Use code with caution. Copied to clipboard Visual Representation Key Concepts to Remember 2D Array Declaration: int[][] board = new int[rows][cols];
Nested Loops: You need an outer loop for rows and an inner loop for columns to access every "cell." Mastering the 9
Modulus Operator (%): This is the most efficient way to toggle between two states (even/odd).
Problem: The squares are outlined but not colored.
Fix: You must call both setFillColor() and setFilled(true).
for i in range(8): row = [] for j in range(8): # Check if the sum of row and column indices is even if (i + j) % 2 == 0: row.append("red") else: row.append("black") board.append(row)
set canvas size (e.g., 400 x 400) set number of rows/cols = 8 square_size = canvas_width / 8
for row from 0 to 7: for col from 0 to 7: x = col * square_size y = row * square_size if (row + col) % 2 == 0: color = RED else: color = BLACK draw square at (x, y) with size square_size, fill color
If you are working through the CodeHS Java course (specifically the "9.1.6 Checkerboard v1" problem), you have likely encountered a classic programming challenge: creating a checkerboard pattern. This exercise is a rite of passage for learning nested loops, conditional logic, and graphical object placement.
In this article, we will break down exactly what the 9.1.6 Checkerboard v1 assignment asks for, how to approach the logic, and provide a fully commented solution.
Input:
Output:
Properties to satisfy:
Complexity constraints:
