Dynamic Programming / 2Dhard70 minBackend Engineer

Routing Grid Reliability DP

Backend Engineer signal: grid DP + path optimization in a service routing context. This is a ProdMatch-owned backend engineer drill, framed as a April 2026 PayPal Core Infra simulation, not a copied platform question.

Company context

PayPal · Core Infra

Freshness

April 2026

Product surface

service routing

ProdMatch interview simulation based on product-team patterns; not a claim of a real company question.

Question

Model service routing as a grid of processing zones. Move only right or down. Return the maximum reliability path score while avoiding blocked cells.

Input

Grid of scores with blocked cells marked -1.

Output

Maximum score from top-left to bottom-right, or -1.

Constraints

1 <= rows, cols <= 1000
Scores may be zero.
Start or end may be blocked.

Concepts

idempotency
queues
rate limiting
grid DP
path optimization
obstacle handling

[[5,1],[2,4]] -> 11

Approach

Try framing your own approach first. The 30 seconds you think before peeking is where learning happens.

Clean Solution

Reveal the approach first.

How well did you understand?

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Common Mistakes

Blocked start/end must be handled before the loop.
Use the impossible sentinel consistently.

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