5 Best Ways to Program to Find the Sum of Elements Forming a Z Shape in a Matrix with Python

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πŸ’‘ Problem Formulation: Given a two-dimensional matrix (a list of lists), the task is to compute the sum of elements forming a Z shape. For instance, in a 3×3 matrix [[1,2,3], [4,5,6], [7,8,9]], the Z-shaped sum would include elements 1, 2, 3, 5, and 7, 8, 9, thus the desired output is 35.

Method 1: Iterative Traversal

This method involves iterating over each row of the matrix to accumulate the sum of the Z shape. The first and last rows are added in their entirety, whereas from the intermediate rows only the element equidistant from the end is added. This method is straightforward and works well with matrices of any size.

Here’s an example:

def z_shape_sum(matrix):
    size = len(matrix)
    total_sum = sum(matrix[0]) + sum(matrix[-1])
    for i in range(1, size-1):
        total_sum += matrix[i][size-1-i]
    return total_sum

# Example matrix
matrix = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]

# Calculate the Z-shape sum
print(z_shape_sum(matrix))

The output of this code is 35.

This code snippet defines a function z_shape_sum() that takes a square matrix and returns the sum of its Z-shaped elements. It first calculates the sum of the first and last rows. Then, it iterates through the middle rows, adding the element that forms part of the Z shape.

Method 2: Using List Comprehension

In Python, list comprehensions provide a concise way to create lists. They consist of brackets containing an expression followed by a for clause, then zero or more for or if clauses. The expressions can be anything, meaning you can put in all kinds of objects in lists. This method leverages list comprehension to calculate the sum in a more Pythonic and compact way.

Here’s an example:

def z_shape_sum(matrix):
    size = len(matrix)
    return sum([matrix[i][i if i == 0 or i == size-1 else size-1-i] for i in range(size)])

# Example matrix
matrix = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]

# Calculate the Z-shape sum
print(z_shape_sum(matrix))

The output of this code is 35.

This code block uses Python list comprehension to condense the function body seen in Method 1. It iterates over the indices and picks the appropriate elements to sum, handling the first and last rows as well as the diagonal element for every intermediate row.

Method 3: Utilizing NumPy Library

For those working within the scientific computing ecosystem of Python, NumPy is a fundamental package for array computing. This method uses NumPy array slicing to sum the Z-shape elements, and is the fastest approach for large matrices.

Here’s an example:

import numpy as np

def z_shape_sum(matrix):
    matrix = np.array(matrix)
    size = matrix.shape[0]
    return matrix[0].sum() + matrix[-1].sum() + matrix[1:-1, size-2:0:-1].diagonal().sum()

# Example matrix as NumPy array
matrix = np.array([[1, 2, 3], [4, 5, 6], [7, 8, 9]])

# Calculate the Z-shape sum
print(z_shape_sum(matrix))

The output of this code is 35.

This function converts a regular list of lists into a NumPy array and uses powerful slicing techniques to sum the first and last rows, as well as the reverse diagonal using diagonal().sum().

Method 4: Pure Python Without Additional Functions

If one wishes to avoid using any additional Python functions, the problem can be solved with pure Python code. This method manually sums the first and last rows, and the diagonally traversed elements, without employing built-in functionalities.

Here’s an example:

def z_shape_sum(matrix):
    size = len(matrix)
    total_sum = 0
    for i in range(size):
        total_sum += matrix[0][i] + matrix[size-1][i] if i < size-1 else 0
        total_sum += matrix[i][size-1-i] if 0 < i < size-1 else 0
    return total_sum

# Example matrix
matrix = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]

# Calculate the Z-shape sum
print(z_shape_sum(matrix))

The output of this code is 35.

Here we directly add the elements using index manipulation and control structures, thus avoiding any Python-specific shortcuts or library functions. This is the manual approach to solving the problem, which provides a deeper understanding of the logic involved.

Bonus One-Liner Method 5: Advanced List Comprehension

For those up for a challenge, Python can accomplish the task in a one-liner using a more complex list comprehension that combines all steps into a single statement. This is the most concise solution but possibly the least readable for newcomers to Python.

Here’s an example:

matrix = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]

# Calculate the Z-shape sum in one line
print(sum(matrix[0] + [row[-(i+1)] for i, row in enumerate(matrix[1:-1])] + matrix[-1]))

The output of this code is 35.

This one-liner accomplishes the sum directly within the print() function call. It sums the first and last rows of the matrix and computes the reverse diagonal on the fly using a list comprehension with enumerate.

Summary/Discussion

  • Method 1: Iterative Traversal. Straightforward and easy to understand. Not the most Pythonic method.
  • Method 2: Using List Comprehension. More concise and Pythonic. Potentially difficult for beginners to read.
  • Method 3: Utilizing NumPy Library. Best performance for large data sets. Requires external library.
  • Method 4: Pure Python without Additional Functions. Provides the deepest understanding of the logic. Verbose and potentially slower.
  • Method 5: Advanced List Comprehension. Most concise solution. Readability might be an issue for those not familiar with Python’s list comprehensions.