DSA problem

Sum of Array Elements Using Recursion

EasyRecursionPattern: RecursionbeginnerFree

Given an array of N integers, compute the sum of all its elements using recursion only.

The key insight: the sum of an array is its first element plus the sum of the rest of the array. The "rest" is represented by passing an index that advances with each call. Base case: when index reaches the array length, return 0. Recursive case: return arr[index] + sumArray(arr, index + 1).

This "handle one element, recurse on the rest" decomposition is the foundation of recursive list processing - how functional languages such as Haskell, Lisp, and Erlang process collections - and it introduces the idea of reducing (folding) a collection to a single value.

Examples

Example 1

Input: arr = [1, 2, 3, 4, 5]

Output: 15

Explanation: 1 + 2 + 3 + 4 + 5 = 15. Each call adds one element and recurses on the remaining suffix until the index passes the end.

Example 2

Input: arr = [-2, 4, 10]

Output: 12

Explanation: -2 + 4 + 10 = 12. Negative values are added just like any other element.

Constraints

1 <= N <= 10^4

3 hints and a full solution walkthrough with step-by-step visualizations are available in the practice editor.

recursionarray

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