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[Hacker Rank] Interview Preparation Kit: Arrays: Array Manipulation. Solved ✅.
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‎algorithm_exercises_csharp/src/hackerrank/interview_preparation_kit/arrays/CrushBruteForce.cs

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/**
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* Crush (Brute Force).
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*
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* @link Problem definition [[docs/hackerrank/interview_preparation_kit/arrays/crush.md]]
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* @link Solution notes [[docs/hackerrank/interview_preparation_kit/arrays/crush_optimized-solution-notes.md]]
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*/
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namespace algorithm_exercises_csharp.hackerrank.interview_preparation_kit;
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using System.Diagnostics.CodeAnalysis;
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public class CrushBruteForce
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{
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[ExcludeFromCodeCoverage]
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protected CrushBruteForce() { }
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private const int INITIALIZER = 0;
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public static long arrayManipulation(int n, List<List<int>> queries)
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{
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// why adding 1?
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// first slot to adjust 1-based index and
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int[] result = new int[n + 1];
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Array.Fill(result, INITIALIZER);
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int maximum = INITIALIZER;
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foreach (List<int> query in queries)
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{
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int start = query[0];
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int end = query[1];
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int value = query[2];
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for (int i = start; i < end + 1; i++)
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{
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result[i] += value;
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}
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foreach (int current in result)
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{
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maximum = Math.Max(current, maximum);
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}
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}
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return maximum;
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}
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}

‎algorithm_exercises_csharp/src/hackerrank/interview_preparation_kit/arrays/CrushOptimized.cs

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/**
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* Crush (Optimized).
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*
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* @link Problem definition [[docs/hackerrank/interview_preparation_kit/arrays/crush.md]]
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* @link Solution notes [[docs/hackerrank/interview_preparation_kit/arrays/crush_optimized-solution-notes.md]]
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*/
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namespace algorithm_exercises_csharp.hackerrank.interview_preparation_kit;
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using System.Diagnostics.CodeAnalysis;
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public class CrushOptimized
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{
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[ExcludeFromCodeCoverage]
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private CrushOptimized() { }
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/**
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* arrayManipulation.
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*/
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public static long arrayManipulation(int n, List<List<int>> queries)
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{
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// why adding 2?
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// first slot to adjust 1-based index and
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// last slot for storing accumSum result
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int[] result = new int[n + 2];
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Array.Fill(result, 0);
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int maximum = 0;
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foreach (List<int> query in queries)
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{
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int a = query[0];
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int b = query[1];
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int k = query[2];
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// Prefix
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result[a] += k;
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result[b + 1] -= k;
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int accumSum = 0;
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foreach (int value in result)
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{
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accumSum += value;
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maximum = Math.Max(maximum, accumSum);
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}
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}
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return maximum;
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}
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}

‎algorithm_exercises_csharp_test/Resources/hackerrank/interview_preparation_kit/arrays/crush.testcases.json

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[
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{
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"title": "Sample Test Case 0",
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"n": 5,
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"queries": [
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[
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1,
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2,
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100
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],
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[
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2,
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5,
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100
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],
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[
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3,
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4,
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100
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]
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],
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"expected": 200
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},
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{
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"title": "Sample Test Case 1",
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"n": 10,
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"queries": [
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[
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1,
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5,
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3
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],
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[
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4,
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8,
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7
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],
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[
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6,
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9,
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1
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]
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],
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"expected": 10
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},
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{
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"title": "Sample Test Case 3",
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"n": 10,
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"queries": [
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[
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2,
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6,
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8
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],
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[
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3,
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5,
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7
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],
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[
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1,
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8,
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1
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],
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[
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5,
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9,
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15
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]
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],
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"expected": 31
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}
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]

‎algorithm_exercises_csharp_test/algorithm_exercises_csharp_test.csproj

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<ItemGroup>
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<EmbeddedResource Include="Resources/hackerrank/interview_preparation_kit/arrays/ctci_array_left_rotation.testcases.json" />
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<EmbeddedResource Include="Resources/hackerrank/interview_preparation_kit/arrays/crush.testcases.json" />
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<EmbeddedResource Include="Resources/hackerrank/interview_preparation_kit/dictionaries_and_hashmaps/ctci_ransom_note.testcases.json" />
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<EmbeddedResource Include="Resources/hackerrank/interview_preparation_kit/dictionaries_and_hashmaps/two_strings.testcases.json" />
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<EmbeddedResource Include="Resources/hackerrank/interview_preparation_kit/greedy_algorithms/luck_balance.testcases.json" />

‎algorithm_exercises_csharp_test/src/hackerrank/interview_preparation_kit/arrays/CrushBruteForce.Test.cs

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namespace algorithm_exercises_csharp.hackerrank.interview_preparation_kit;
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[TestClass]
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public class CrushBruteForceTest
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{
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public class CrushBruteForceTestCase
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{
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public string title { get; set; } = default!;
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public List<List<int>> queries { get; set; } = default!;
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public int n { get; set; } = default!;
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public long expected { get; set; } = default!;
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}
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private List<CrushBruteForceTestCase> testCases { get; set; } = default!;
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[TestInitialize]
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public void testInitialize()
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{
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testCases = JsonLoader.resourceLoad<List<CrushBruteForceTestCase>>(
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"hackerrank/interview_preparation_kit/arrays/crush.testcases.json"
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) ?? [];
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}
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[TestMethod]
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public void testArrayManipulation()
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{
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long result;
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foreach (CrushBruteForceTestCase test in testCases)
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{
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result = CrushBruteForce.arrayManipulation(test.n, test.queries);
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Assert.AreEqual(test.expected, result);
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}
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}
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}
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‎algorithm_exercises_csharp_test/src/hackerrank/interview_preparation_kit/arrays/CrushOptimized.Test.cs

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namespace algorithm_exercises_csharp.hackerrank.interview_preparation_kit;
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[TestClass]
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public class CrushOptimizedTest
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{
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public class CrushOptimizedTestCase
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{
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public string title { get; set; } = default!;
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public List<List<int>> queries { get; set; } = default!;
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public int n { get; set; } = default!;
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public long expected { get; set; } = default!;
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}
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private List<CrushOptimizedTestCase> testCases { get; set; } = default!;
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[TestInitialize]
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public void testInitialize()
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{
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testCases = JsonLoader.resourceLoad<List<CrushOptimizedTestCase>>(
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"hackerrank/interview_preparation_kit/arrays/crush.testcases.json"
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) ?? [];
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}
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[TestMethod]
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public void testArrayManipulation()
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{
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long result;
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foreach (CrushOptimizedTestCase test in testCases)
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{
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result = CrushOptimized.arrayManipulation(test.n, test.queries);
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Assert.AreEqual(test.expected, result);
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}
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}
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}
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‎docs/hackerrank/interview_preparation_kit/arrays/crush.md

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# [Arrays: Array Manipulation](https://www.hackerrank.com/challenges/crush)
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Perform m operations on an array and print the maximum of the values.
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- Difficulty: `#hard`
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- Category: `#ProblemSolvingIntermediate` `#arrays`
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Starting with a 1-indexed array of zeros and a list of operations, for each
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operation add a value to each the array element between two given indices,
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inclusive. Once all operations have been performed, return the maximum
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value in the array.
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## Example
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Queries are interpreted as follows:
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```text
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a b k
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1 5 3
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4 8 7
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6 9 1
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```
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Add the values of between the indices and inclusive:
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```text
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index-> 1 2 3 4 5 6 7 8 9 10
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[0,0,0, 0, 0,0,0,0,0, 0]
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[3,3,3, 3, 3,0,0,0,0, 0]
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[3,3,3,10,10,7,7,7,0, 0]
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[3,3,3,10,10,8,8,8,1, 0]
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```
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The largest value is `10` after all operations are performed.
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## Function Description
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Complete the function arrayManipulation in the editor below.
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arrayManipulation has the following parameters:
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- `int n` - the number of elements in the array
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- `int queries[q][3]` - a two dimensional array of queries where
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each `queries[i]` contains three integers, `a`, `b`, and `k`.
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## Returns
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- int - the maximum value in the resultant array
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## Input Format
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The first line contains two space-separated integers `n` and `m`, the size of
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the array and the number of operations.
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Each of the next `m` lines contains three space-separated integers
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`a`, `b` and `k`, the left index, right index and summand.
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## Constraints
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- $ 3 \leq n \leq 10^7 $
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- $ 1 \leq m \leq 2*10^5 $
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- $ 1 \leq a \leq b \leq n $
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- $ 0 \leq k \leq 10^9 $
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## Sample Input
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```text
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5 3
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1 2 100
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2 5 100
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3 4 100
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```
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## Sample Output
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```text
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200
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````
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## Explanation
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After the first update the list is `100 100 0 0 0`.
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After the second update list is `100 200 100 100 100`.
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After the third update list is `100 200 200 200 100`.
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The maximum value is `200`.

‎docs/hackerrank/interview_preparation_kit/arrays/crush_optimized-solution-notes.md

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# [Array Manipulation](https://www.hackerrank.com/challenges/crush)
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Perform m operations on an array and print the maximum of the values.
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- Difficulty: `#hard`
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- Category: `#ProblemSolvingIntermediate` `#arrays`
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## Solution sources
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### Brute force idea
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The first solution attempt is based on the idea of going through:
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> each row and then,
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> > each sub-set of elements affected by the operation.
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With this principle, the algorithm becomes O(N^2)
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### Optimized
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Reading about posible optimizations,
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I found the possibility of summarizing the interior traversal with
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addition operations for each element in each row of operations,
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in only 2 constant operations, which represents the necessary values so that
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in a single final traversal, the sum values can be obtained "by drag".
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The algorithm is called "prefix sum."
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Some sources about "prefix sum"
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- <https://hmn.wiki/en/Prefix_sum>
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- <https://en.wikipedia.org/wiki/Prefix_sum>
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- <https://usaco.guide/silver/prefix-sums?lang=py>
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Some sources about implementation in:
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- [HackerRank Array Manipulation — beat the clock using Prefix Sum (JavaScript)](https://medium.com/@mlgerardvla/hackerrank-array-manipulation-beat-the-clock-using-prefix-sum-92471060035e)
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- [Hackerrank Discussions Forums: Array Manipulation](https://www.hackerrank.com/challenges/one-month-preparation-kit-crush/forum)

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