Amazon OA Sharing | Analysis and Summary of Amazon Online Assessment Questions + HackerRank Solutions

Guiding students through a recent game Amazon Online Assessment, I'd like to share some experience. This OA had a moderate overall difficulty and the questions were well-aligned with Amazon's business scenarios, testing the application of combination mathematics and greedy algorithms. I hope this sharing can help those preparing for it!

Timeline and Exam Format

Important Note:none:

• The problem has hidden test cases; do not submit based solely on sample cases.
• It is recommended to go through both questions quickly and select those that you feel confident about answering first.
• Time allocation: First question recommended to take 50-60 minutes, second question in 30-40 minutes, leaving 10-15 minutes for checking.

题目 1：仓库机器人配置计数

题目描述

在亚马逊仓库中，有 n 个机器人，每个机器人可以是运行（Operating）或待机（Standby）状态。每个机器人 I 有一个协调阈值 coordinationThreshold[i].

故障条件（满足任一即故障）：

1. 机器人 I 正在运行，但其他运行中的机器人数量 < coordinationThreshold[i]
2. 机器人 I 处于待机，但运行中的机器人总数 ≥ coordinationThreshold[i]

目标：计算有多少种配置方案，使得没有任何机器人故障。

Question 1: Approach

Core is: Let the total number of running robots be kWe can enumerate through k The number of possible solutions can be calculated based on their potential values:

1. For a fixed kIdentify all robots that must be running and those that must standby.
   • 机器人 I Must be run:CoordinationThreshold[i] ≤ k - 1
   • 机器人 I Must be powered on standby:CoordinationThreshold[i] > k
   • 机器人 I Optional:K - 1 < coordinationThreshold[i] ≤ k
2. If the number of selectable robots is mThen, there is a condition such that "the number of robots that must be run ≤ k ≤ the number of required robots + the number of optional robots" holds. C(m, k) Propose a plan
3. Exploring all possibilities kI'm unable to provide a translation as the input text is incomplete and does not contain any meaningful content. Please provide a complete sentence or paragraph in Chinese for me to translate it into fluent English.0 ≤ k ≤ nSum all valid solution numbers.

Reference code

Import math from math import comb

Def countValidConfigurations(n, coordinationThreshold)
Total_configs = 0

# Enumerate the total number of robots, k
for k in range(n + 1):
    must_operate = 0    # Must operate
    must_standby = 0   # Must standby
    flexible = 0       # Flexible

    for i in range(n):
        threshold = coordinationThreshold[i]

        # If operating is required, at least 'threshold' other robots need to be running
        # When the total number of operational robots is k, the count of other operational robots = k - 1
        if threshold <= k - 1:
            # Threshold  k:
                # However, standby would also fail (since k >= threshold for all operational robots)
                must_operate += 1
            else:
                # For 'threshold'  k-1 implies failure when operating
            if threshold > k:
                # Standby does not fail in this case
                must_standby += 1
            else:
                # For k-1 < threshold <= k, both operation and standby would fail
                # This configuration is unfeasible; skip to the next 'k'
                must_standby = float('inf')
                break

    # Check feasibility
    if must_operate <= k <= must_operate + flexible:
        # Choose (k - must_operate) robots out of the flexible group for operation
        configs = comb(flexible, k - must_operate)
        total_configs += configs

return total_configs

N equals 8
CoordinationThreshold = [6, 0, 3, 3, 6, 7, 2, 7]
Print(countValidConfigurations(n, coordinationThreshold)) # Output: 3

题目 2：服务器算力调整

题目描述

AWS 有 n 台服务器，初始算力为 Power [n]。需要通过调整让算力数组变成非递减排列。

调整规则:none:

• 可以选择任意连续子数组 [L,R]，给这些服务器同时增加 x 点算力（X ≥ 0）
• 可以执行多次操作

目标：找到最小的所有操作的 x 之和。

Topic 2: Approach

This is the classic "use interval addition to make an array non-decreasing and find the minimum sum of increments" problem, with the optimal solution being through difference/ greedy methods.

• Traverse the array from left to right, if Power[i] is less than power[i-1]Then Power[i] Additional needs to be added Delta = power[i - 1] - power[i]
• To minimize operands, we could directly provide Power[i] Increase DeltaEquivalent to [i, n-1] None The provided text "加" is a single Chinese character that translates to "add" in English. If you intended to provide more context or a complete sentence including this character, please rephrase your input. Delta）
• Sum all Delta It is sufficient to add up all the values (since the effect of interval addition is equivalent to adding individual elements without affecting subsequent non-decreasing checks).

Reference code

Def findMinimumSum(power):
    n = len(power)
    total_increase = 0
    
    for i in range(1, n):
        if power[i] = 3, no change
# i=2: 1 = 4, no change
# i=4: 2 < 6, add 4 → [3, 4, 4, 6, 6], total += 4
# Final answer: 3 + 4 = 7

Recommended Study Materials

• Similar Problems on LeetCode:none:
  • The first question is similar to:LeetCode 1434: Number of Ways to Wear Different Hats(Enum States)
  • The second question is similar to:LeetCode 1827: Minimize Operations to Make Array Increasing
• Key review:none:
  • Combinatorics (permutations and combinations, principle of inclusion-exclusion)
  • Greedy Algorithms (Interval Problems and Scheduling Problems)
  • Differencing Arrays and Prefix Sums

Some Additional Tips for Preparing for Big Company Interviews

Amazon OA appears to typically consist of only two questions, but the actual execution puts a lot of pressure – not just from hidden test cases, but also requiring quick thinking for optimal solutions. Especially for companies like Amazon that frequently use platforms such as HackerRank / CodeSignal, many students get stuck not due to basic syntax errors, but rather:

• Understanding speed is slow.
• Edge cases are easily overlooked.
• Debugging takes too long.
• It was on the right track logically, but ultimately failed all the test cases.

If you are preparing for Amazon OA, VO, or other large company technical interviews, ProgramHelp provides more comprehensive support:

• OA real-time assistance
• HackerRank / CodeSignal support
• Mock interviews
• Technical interview guidance
• System design preparation
• Amazon Leadership Principles interview prep

If you have recently been preparing for positions at major companies like Amazon, TikTok, Meta, and Google, early preparation would definitely make things much easier.

If you have recently been preparing for positions at major firms like Amazon, TikTok, Meta, and Google, thorough preparation will certainly make things much easier.

Jory Wang Senior Software Engineer at Amazon

Senior Engineer at Amazon, specializing in the development of core systems within infrastructure, with extensive practical experience in system scalability, reliability, and cost optimization. Currently focused on FAANG SDE interview preparation, assisting over 30 candidates in securing L5/L6 offers within a year.

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