Microsoft 26NG SDE OA Interview | Two questions full AC thinking analysis + summary of high-frequency test points

This time Microsoft 26NG SDE OA, the overall difficulty is still relatively basic, but clear thinking + speed of implementation are the key. Many students will underestimate Microsoft OA, but in fact the main sticking points are in detail processing and time allocation.

I did it in the morning this time, and the two questions took about 20 minutes to go directly to AC, and the pace was very smooth. Simply organize the questions and core ideas to provide a reference for students who want to do it later.

T1: Jump maximum score

Question description

The player starts from index 0 and reaches the goal n-1. Each time you can:

• Move 1 step to the right
• Or jump p steps to the right (p is a prime number whose ones digit is 3)

Each time a position is reached, the points for that position will be accumulated to find the maximum total score.

Core idea

The essence of this question is a one-dimensional DP + special step size set:

Step 1: Preprocess all steps that meet the conditions

• Exist [1,n] Sieve prime numbers in range (Ehrstein sieve)
• Filter out prime numbers with units digit 3 (such as 3, 13, 23, …)

Step 2: DP transfer

• Definition Dp[i] Represents the maximum score to reach i
• Initialization:Dp[0] = score[0]

Transfer logic: From i you can go to:

• I+1
• I+p(p belongs to the set of legal prime numbers)

Update: dp[j] = max(dp[j], dp[i] + score[j])

T2: Minimal operation to change n to 0

Question description

Given a positive integer n, each time you can:

• Add or subtract one 2^i

Find the minimum number of operations such that n becomes 0.

Core idea

This question is actually a variation of the classic question. The essence is:

Convert n to non-adjacent form (NAF)
Or understood as "binary greedy with carry"

Greedy strategy

Processing starting from the lowest bit:

• If n is an even number → shift right directly
• If n is odd:
  • Look at the last two:
    • 01 → Decrease 1 (to 00)
    • 11 → Add 1 (better to trigger carry)

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Jory Wang Amazon Senior Software Development Engineer

Amazon senior engineer, focusing on the research and development of infrastructure core systems, with rich practical experience in system scalability, reliability and cost optimization. Currently focusing on FAANG SDE interview coaching, helping 30+ candidates successfully obtain L5/L6 Offers within one year.

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