Matrix Addition - codepath/compsci_guides GitHub Wiki

TIP102 Unit 1 Session 2 Advanced (Click for link to problem statements)

Problem Highlights

• 💡 Difficulty: Easy
• ⏰ Time to complete: 10 mins
• 🛠️ Topics: Arrays, Matrix Manipulation

U-nderstand

Understand what the interviewer is asking for by using test cases and questions about the problem.

• Q: What is the input to the function?

  • A: The input consists of two n x m matrices matrix1 and matrix2.

• Q: What is the expected output of the function?

  • A: The function should return an n x m matrix sum_matrix, where each element is the sum of the corresponding elements from matrix1 and matrix2.

• Q: What should the function return if the matrices are empty?

  • A: If the input matrices are empty, the function should return an empty matrix.

• Q: Are the matrices guaranteed to have the same dimensions?

  • A: Yes, the problem assumes that both matrices have the same dimensions.

• The function add_matrices() should take two matrices of the same dimensions and return a new matrix where each element is the sum of the corresponding elements in the two input matrices.

HAPPY CASE
Input: 
matrix1 = [[1, 2, 3], 
           [4, 5, 6], 
           [7, 8, 9]]
matrix2 = [[9, 8, 7], 
           [6, 5, 4], 
           [3, 2, 1]]
Expected Output: 
[[10, 10, 10], 
 [10, 10, 10], 
 [10, 10, 10]]

EDGE CASE
Input: 
matrix1 = [1](/codepath/compsci_guides/wiki/1)
matrix2 = [1](/codepath/compsci_guides/wiki/1)
Expected Output: [2](/codepath/compsci_guides/wiki/2)

P-lan

Plan the solution with appropriate visualizations and pseudocode.

General Idea: Iterate through both matrices and sum the corresponding elements to create a new matrix.

1. Get the dimensions of the matrices (rows and columns).
2. Initialize a new sum matrix with the same dimensions, filled with zeros.
3. Loop through each row and column:
   a. Sum the corresponding elements from matrix1 and matrix2.
   b. Store the result in the sum matrix.
4. Return the sum matrix

⚠️ Common Mistakes

• Forgetting to ensure both matrices are of the same size.
• Not properly initializing the sum matrix.

I-mplement

Implement the code to solve the algorithm.

def add_matrices(matrix1, matrix2):
    # Get the dimensions of the matrices
    rows = len(matrix1)
    cols = len(matrix1[0])
    
    # Initialize the sum matrix with zeros
    sum_matrix = []
    for _ in range(rows):
        sum_matrix.append([0] * cols)
    
    # Iterate through each element and sum the corresponding elements
    for i in range(rows):
        for j in range(cols):
            sum_matrix[i][j] = matrix1[i][j] + matrix2[i][j]
    
    return sum_matrix