Python Program to Find the Sum of Elements in a List Recursively

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Lists in Python:

A list is a Python data type that can be used in a variety of ways. A list is made up of comma-separated values, which are referred to as list items. Within square brackets, a list is declared. It’s worth noting that elements in a list don’t have to be of the same type.

Recursion:

If you’re familiar with Python functions, you’ll know that it’s typical for one function to call another. It is also feasible for a function in Python to call itself! A recursive function calls itself, and the process of using a recursive function is known as recursion.

Although it may appear strange for a function to call itself, many sorts of programming challenges are better stated recursively.

Given a list, the task is to find the sum of the list using recursion in Python.

Examples:

Example1:

Input:

given list = 9, 1, 27, 48, 91, 93, 99, 27, 29, 33, 39, 19, 11, 27, 29, 35, 39, 12, 65, 69, 67

Output:

The sum of the given list
 [9, 1, 27, 48, 91, 93, 99, 27, 29, 33, 39, 19, 11, 27, 29, 35, 39, 12, 65, 69, 67] 
with size  21  = 869

Example2:

Input:

given list =11 13 21 85 34 96 75 73 14 25 37 39 49 47 65 69 63 21 29 123 456 789

Output:

The sum of the given list
[11, 13, 21, 85, 34, 96, 75, 73, 14, 25, 37, 39, 49, 47, 65, 69, 63, 21, 29, 123, 456, 789] 
with size 22 = 2234

Program to Find the Sum of Elements in a List Recursively in Python

Below are the ways to Find the Sum of Elements in a List using the recursive approach in Python:

Using Recursion(Static Input)
Using Recursion(User Input)

1)Using Recursion (Static Input)

Approach:

Give the input of the list as static input and store it in a variable.
Calculate the size of the list using the len() function and store it in a variable.
Create a recursive function that accepts an array and its size as parameters.
The recursive function will take the list and its size as inputs.
Return 0 if the list’s length is zero.
Otherwise, along with the recursive function call, return the sum of the last entry of the list (with the size reduced by 1).
The final sum is printed when the returned result is saved in a variable.
The exit of the Program.

Below is the implementation:

# function which accepts the given list and list size
# as parameters and calculates the sum of the given list using recursion


def sumListRecursion(given_list, sizeOflist):
  # Return 0 if the list's length is zero.(base condition)
    if (sizeOflist == 0):
        return 0
    else:
      # Otherwise, along with the recursive function call,
      # return the sum of the last entry of the list (with the size reduced by 1).

        return given_list[sizeOflist-1] + sumListRecursion(given_list, sizeOflist-1)


# Give the input of the list as static input and store it in a variable.
given_list = [9, 1, 27, 48, 91, 93, 99, 27, 29,
              33, 39, 19, 11, 27, 29, 35, 39, 12, 65, 69, 67]
# Calculate the size of the list using len() function and store it in a variable.
sizeOflist = len(given_list)
# passing the given list and sizeOflist as arguments to the recursive function sumListRecursion.
print('The sum of the given list\n', given_list, '\nwith size ',
      sizeOflist, ' =', sumListRecursion(given_list, sizeOflist))

Output:

The sum of the given list
 [9, 1, 27, 48, 91, 93, 99, 27, 29, 33, 39, 19, 11, 27, 29, 35, 39, 12, 65, 69, 67] 
with size  21  = 869

2)Using Recursion (User Input separated by spaces)

Approach:

Scan the given list using map,input(),list() and split() functions.
Calculate the size of the list using the len() function and store it in a variable.
Create a recursive function that accepts an array and its size as parameters.
The recursive function will take the list and its size as inputs.
Return 0 if the list’s length is zero.
Otherwise, along with the recursive function call, return the sum of the last entry of the list (with the size reduced by 1).
The final sum is printed when the returned result is saved in a variable.
The exit of the Program.

Below is the implementation:

# function which accepts the given list and list size
# as parameters and calculates the sum of the given list using recursion


def sumListRecursion(given_list, sizeOflist):
  # Return 0 if the list's length is zero.(base condition)
    if (sizeOflist == 0):
        return 0
    else:
      # Otherwise, along with the recursive function call,
      # return the sum of the last entry of the list (with the size reduced by 1).

        return given_list[sizeOflist-1] + sumListRecursion(given_list, sizeOflist-1)


# Scan the given list using map,input(),list() and split() functions.
given_list = list(map(int, input(
    'Enter some random integer elements to the list separated by spaces = ').split()))
# Calculate the size of the list using len() function and store it in a variable.
sizeOflist = len(given_list)
# passing the given list and sizeOflist as arguments to the recursive function sumListRecursion.
print('The sum of the given list\n', given_list, '\nwith size ',
      sizeOflist, ' =', sumListRecursion(given_list, sizeOflist))

Output:

Enter some random integer elements to the list separated by spaces =
 11 13 21 85 34 96 75 73 14 25 37 39 49 47 65 69 63 21 29 123 456 789
The sum of the given list
[11, 13, 21, 85, 34, 96, 75, 73, 14, 25, 37, 39, 49, 47, 65, 69, 63, 21, 29, 123, 456, 789] 
with size 22 = 2234

Explanation:

A recursive function is called using the list and its size as parameters.
If the function’s size reduces to zero, 0 is returned.
Otherwise, the recursive function call (with the size reduced by 1) is returned, along with the sum of the last entry of the list.
The returned values are saved in a list, and the sum of the list’s items is printed using the print() function.

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