Python program to find the sum of a Sublist

Given a list of numbers, write a Python program to find the sum of all the elements in the list.

Examples:

Input: arr = [2,4,5,10], i = 1, j = 3
Output: 19

Input: arr = [4,10,5,3,3], i = 3, j = 3
Output: 3

Find the sum of a Sublist Applying Brute Force 

In this method, we will be initializing an output variable, say ans=0. Then initialize a loop from index i to j and add the list element to the output.

Python3

# Giving Input list and start-end
# index values
l = [4, 10, 5, 3, 3]
i = 3
j = 3

# Initializing an output variable
# as 0
ans = 0

# Loop start from i to j+1
for i in range(i, j+1):
    ans += l[i]

# Printing result
print(ans)

Output: 

3

Time Complexity: O(n)
Auxiliary Space: O(1)

Find the sum of a Sublist By using the Cumulative Technique

The cumulative sum technique is used to add all the previous element values to the current index value.

Python3

# Giving Input list and start-end
# index values
l = [2, 4, 5, 10]
i = 1
j = 3

# Loop starts
# Adding the previous values
# At every location
for x in range(len(l)):
    if(x == 0):
        continue
    else:
        l[x] = l[x]+l[x-1]

# Printing result
if(i == 0):
    print(l[j])
else:
    print(l[j]-l[i-1])

Output : 

19

Find the sum of a Sublist By using sum() function

 sum() function is used to calculate the sum of the list. It takes input as the sub-list.

Python3

# Giving input list and start-end
# index values
l = [2, 4, 5, 10]
i = 1
j = 3

# Prints sum of sublist from index
# i to index j
print(sum(l[i:j+1]))

Output : 

19

Time Complexity: O(n)
Auxiliary Space: O(n), where n is number of elements in list.

Find the sum of a Sublist By using Math Module

Math module has a special function name fsum(). It also takes the input as the sublist. Then we can use fsum() function, to calculate the sum of the sub-list.

Python3

# Input list and start-end index values
l = [4, 10, 5, 3, 3]
i = 3
j = 3

# Applying fsum() function
# i to index j
sum = math.fsum(l[i:j+1])
print(sum)

Output :

3 

Find the sum of a Sublist using Recursion

A new approach to finding the sum of a sublist would be to use recursive programming, where a recursive function is called on itself to continually add the current element of the sublist to a running total until the end of the sublist is reached.

Python3

def sublist_sum(l, i, j):

    # base case
    if (i == j):
        return l[i]

    # recursive step
    return l[i] + sublist_sum(l, i + 1, j)

# Driver code
l = [2, 4, 5, 10]
i = 1
j = 3
print(sublist_sum(l, i, j))
#This code is contributed by Edula Vinay Kumar Reddy

 Time complexity of the sublist_sum() function is O(n), where n is the length of the input list, 
Auxiliary Space: O(n).

Find the sum of a Sublist using Slice notation

This problem can be solved using Python’s slice notation. This method allows you to extract a portion of the list between the start and end indices, and then use the built-in sum() function to calculate the sum of the sublist.

Python3

l = [4, 10, 5, 3, 3]
i = 3
j = 3

# Using slice notation to get sublist
sublist = l[i:j+1]

# Using sum() function to get sum of sublist
ans = sum(sublist)

# Printing result
print(ans)

Output

3

Time Complexity: O(n)
Auxiliary Space: O(1)