ITPEC FE Subject B October 2025 Question 3

The outer loop fixes the start index, the inner loop extends end from start to N, accumulating sum ← sum + arr[end] at each step.

• •Blank A = `N`: the inner loop must reach the last element, so end runs from start to N (1-indexed array of size N)
• •Blank B = `sum + arr[end]`: each iteration adds the current element arr[end] to the running sum to build the subarray sum incrementally

The early exit (elseif sum > targetSum → exit) is valid because all elements are positive integers — once the sum exceeds the target, extending further only increases it.

Why not others:
- arr[end] alone (no accumulation) — only checks single elements, not subarrays
- sum + arr[start] — adds the wrong element; start is fixed in the inner loop
- N - 1 as upper bound — skips the last array element
- targetSum as upper bound — meaningless as a loop index bound

Key rule: For subarray sum problems with positive integers, the sliding/expanding window works because sums are monotonically increasing as the window grows.

AI-generated — may contain errors