American Express On-Campus OA Experience (2026) | Summer Internship
Summary
I appeared for the American Express on‑campus OA for a Summer Internship; the coding round consisted of three implementation‑heavy questions, two of which I describe below.
Full Experience
Appeared for the American Express on-campus OA on 13th August 2026 for the Summer Internship role. The coding round had 3 questions, and it was quite implementation-heavy overall. I don't remember the 3rd question well.
Question 1
Given an array A of n integers (both positive and negative), choose two contiguous fragments — one of size K and one of size L. The two fragments may overlap. Each element contributes to the final sum only once: if it lies in only one of the two fragments, it's added with its original sign; if it lies in both fragments, it's added with its sign flipped (negated). Find the maximum possible sum.
Function signature: int solution(vector &A, int K, int L)
Example: A = [1, 3, -4, 2, -2], K = 3, L = 2 Fragments: [1, 3, -4] (indices 0-2) and [-4, 2] (indices 2-3) Index 2 (-4) is shared → contributes as +4 Result: 1 + 3 + 4 + 2 = 10
Closest LeetCode: 1031 (Maximum Sum of Two Non-Overlapping Subarrays) — but this variant allows overlap with a sign‑flip twist, so it's a harder version.
Question 2
Given an N x M boolean grid representing a map, where A[R][C] = true means a solar power plant can be built on that cell, and false means it cannot. Place two square‑shaped power plants such that:
Both squares are the same size Every cell inside each square is true The two squares do not share any cell (no overlap) A single cell (1×1) counts as a valid square
Find the maximum possible side length of the two equal squares. Constraints: N, M ≤ 700.
Closest LeetCode: 221 (Maximal Square) — but this only covers the base DP.
Interview Questions (2)
Maximum Sum with Overlapping Subarrays and Sign Flip
Given an array A of n integers (both positive and negative), choose two contiguous fragments — one of size K and one of size L. The two fragments may overlap. Each element contributes to the final sum only once: if it lies in only one of the two fragments, it's added with its original sign; if it lies in both fragments, it's added with its sign flipped (negated). Find the maximum possible sum.
Function signature: int solution(vector &A, int K, int L)
Example: A = [1, 3, -4, 2, -2], K = 3, L = 2 Fragments: [1, 3, -4] (indices 0-2) and [-4, 2] (indices 2-3) Index 2 (-4) is shared → contributes as +4 Result: 1 + 3 + 4 + 2 = 10
Closest LeetCode: 1031 (Maximum Sum of Two Non-Overlapping Subarrays) — but this variant allows overlap with a sign‑flip twist.
Maximum Side Length of Two Equal Non‑Overlapping Squares in Boolean Grid
Given an N x M boolean grid representing a map, where A[R][C] = true means a solar power plant can be built on that cell, and false means it cannot. Place two square‑shaped power plants such that:
- Both squares are the same size
- Every cell inside each square is true
- The two squares do not share any cell (no overlap)
- A single cell (1×1) counts as a valid square
Find the maximum possible side length of the two equal squares. Constraints: N, M ≤ 700.
Closest LeetCode: 221 (Maximal Square) — but this only covers the base DP.