Prefix Sum Range Query

L4 Easy Sliding Window

Concept

Build a prefix-sum array once, and any range sum becomes a single subtraction — O(1) per query no matter how large the range is.

Given an array nums and two indices left and right (inclusive), return the sum of the elements between those indices. If the array is empty, return 0.

Examples

▸ nums = [-2, 0, 3, -5, 2, -1], left = 0, right = 2

→ 1

▸ nums = [-2, 0, 3, -5, 2, -1], left = 2, right = 5

→ -1

▸ nums = [2, 4, 6, 8], left = 1, right = 2

→ 10

Progressive Hints

Hint 1 · Nudge

Precompute once, then answer every range instantly with a subtraction.

Hint 2 · Plan

Build a prefix array where prefix[i] is the sum of the first i elements, with prefix[0] = 0. The inclusive range sum from left to right is prefix[right + 1] - prefix[left]. Return 0 when the array is empty.

Hint 3 · Approach

If nums is empty, return 0. Build prefix with prefix[0] = 0 and prefix[i + 1] = prefix[i] + nums[i]. Return prefix[right + 1] - prefix[left].

Output

// Run your code to see the output here.