Simple sum
Input
[1, 2, 3]
Output
6
1 + 2 + 3 = 6
Full lesson preview
Compute the sum of an array recursively
Implement a recursive function to compute the sum of elements in a list.
Python practice6 minRecursion & BacktrackingBeginnerLast updated March 27, 2026
Problem statement
Write a function that takes a list of integers and returns the sum of its elements using recursion. You may not use loops (for/while) or the built-in sum function. Handle the empty list by returning 0.
Task
Reinforce thinking recursively by summing array elements without using loops or built-in sum.
Examples
Input format
A list of integers, e.g. [1, 2, 3].
Output format
An integer representing the sum of the list elements.
Constraints
Length of list <= 1000 (recursion depth in Python may be limited; practice uses small inputs).
Samples
Sample 1
Input
[]
Output
0
Empty list sums to 0.