Python Program to Find the Sum of an Array

Finding the sum of an array is a fundamental operation in programming. Python provides multiple ways to achieve this, ranging from simple loops to built-in functions and advanced techniques like recursion and functional programming. This article explores different methods to compute the sum of an array in Python.

Example

Consider an array:

arr = [5, 8, 12, 20]

The sum of the elements is:

5 + 8 + 12 + 20 = 45

We will explore various approaches to compute this sum.

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1. Using a Loop (Iterative Method)

The simplest way to find the sum of an array is to iterate through its elements and accumulate their sum.

# Function to calculate sum using a loop
def sum_array(arr):
    total = 0
    for num in arr:
        total += num
    return total

# Example usage
arr = [5, 8, 12, 20]
print("Sum of the array is", sum_array(arr))

Output:

Sum of the array is 45

Time Complexity: O(n)

Auxiliary Space: O(1)

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2. Using Python’s Built-in sum() Function

Python provides an inbuilt function sum() that directly computes the sum of an iterable.

arr = [5, 8, 12, 20]
print("Sum of the array is", sum(arr))

Output:

Sum of the array is 45

Time Complexity: O(n)

Auxiliary Space: O(1)

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3. Using the reduce() Function

The reduce() function from the functools module applies a function cumulatively to the elements of an iterable.

from functools import reduce

arr = [5, 8, 12, 20]
result = reduce(lambda x, y: x + y, arr)
print("Sum of the array is", result)

Output:

Sum of the array is 45

Time Complexity: O(n)

Auxiliary Space: O(1)

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4. Using Recursion

A recursive function can be used to compute the sum by breaking down the array into smaller parts.

def recursive_sum(arr, n):
    if n == 0:
        return 0
    return arr[n - 1] + recursive_sum(arr, n - 1)

arr = [5, 8, 12, 20]
print("Sum of the array is", recursive_sum(arr, len(arr)))

Output:

Sum of the array is 45

Time Complexity: O(n)

Auxiliary Space: O(n) (due to recursive call stack)

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5. Using enumerate()

The enumerate() function helps iterate over the array while keeping track of indices.

arr = [5, 8, 12, 20]
sum_value = sum(a for i, a in enumerate(arr))
print("Sum of the array is", sum_value)

Output:

Sum of the array is 45

Time Complexity: O(n)

Auxiliary Space: O(1)

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6. Using Divide and Conquer (Recursive Approach)

This approach splits the array into halves, computes the sum of each half recursively, and combines the results.

def sum_of_array(arr, low, high):
    if low == high:
        return arr[low]
    mid = (low + high) // 2
    left_sum = sum_of_array(arr, low, mid)
    right_sum = sum_of_array(arr, mid + 1, high)
    return left_sum + right_sum

arr = [5, 8, 12, 20]
print("Sum of the array is", sum_of_array(arr, 0, len(arr)-1))

Output:

Sum of the array is 45

Time Complexity: O(n)

Auxiliary Space: O(log n) (due to recursive call stack)

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7. Using the Counter Method

The Counter class from collections helps count occurrences of elements and calculate the sum efficiently.

from collections import Counter

arr = [5, 8, 12, 20]
c = Counter(arr)
result = sum(k * v for k, v in c.items())
print("Sum of the array is", result)

Output:

Sum of the array is 45

Time Complexity: O(n)

Auxiliary Space: O(n) (due to Counter storage)

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Conclusion

This article explored multiple ways to find the sum of an array in Python. The best method depends on the use case:

• For simplicity: Use sum(arr)
• For functional programming: Use reduce()
• For recursion-based solutions: Use recursive_sum() or Divide and Conquer
• For advanced counting: Use Counter

Each method provides a unique perspective on solving this common problem efficiently.