Merge pull request #467 from sir-gon/feature/crush

[Hacker Rank] Interview Preparation Kit: Arrays: Array Manipulation. …

Author: sir-gon

docs/hackerrank/interview_preparation_kit/arrays/crush.md

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+# [Arrays: Array Manipulation](https://www.hackerrank.com/challenges/crush)
+
+Perform m operations on an array and print the maximum of the values.
+
+- Difficulty:  ` #hard `
+- Category: ` #ProblemSolvingIntermediate `
+
+Starting with a 1-indexed array of zeros and a list of operations, for each
+operation add a value to each the array element between two given indices,
+inclusive. Once all operations have been performed, return the maximum
+value in the array.
+
+## Example
+
+Queries are interpreted as follows:
+
+```text
+    a b k
+    1 5 3
+    4 8 7
+    6 9 1
+```
+
+Add the values of  between the indices  and  inclusive:
+
+```text
+index->  1 2 3  4  5 6 7 8 9 10
+        [0,0,0, 0, 0,0,0,0,0, 0]
+        [3,3,3, 3, 3,0,0,0,0, 0]
+        [3,3,3,10,10,7,7,7,0, 0]
+        [3,3,3,10,10,8,8,8,1, 0]
+```
+
+The largest value is `10` after all operations are performed.
+
+## Function Description
+
+Complete the function arrayManipulation in the editor below.
+
+arrayManipulation has the following parameters:
+
+- `int n` - the number of elements in the array
+- `int queries[q][3]` - a two dimensional array of queries where
+each `queries[i]` contains three integers, `a`, `b`, and `k`.
+
+## Returns
+
+- int - the maximum value in the resultant array
+
+## Input Format
+
+The first line contains two space-separated integers `n` and `m`, the size of
+the array and the number of operations.
+Each of the next `m` lines contains three space-separated integers
+`a`, `b` and `k`, the left index, right index and summand.
+
+## Constraints
+
+- $ 3 \leq n \leq 10^7 $
+- $ 1 \leq m \leq 2*10^5 $
+- $ 1 \leq a \leq b \leq n $
+- $ 0 \leq k \leq 10^9 $
+
+## Sample Input
+
+```text
+5 3
+1 2 100
+2 5 100
+3 4 100
+```
+
+## Sample Output
+
+```text
+200
+````
+
+## Explanation
+
+After the first update the list is `100 100 0 0 0`.
+After the second update list is `100 200 100 100 100`.
+After the third update list is `100 200 200 200 100`.
+
+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)
+
+Perform m operations on an array and print the maximum of the values.
+
+- Difficulty:  ` #hard `
+- Category: ` #ProblemSolvingIntermediate `
+
+## Solution sources
+
+### Brute force idea
+
+The first solution attempt is based on the idea of going through:
+
+> each row and then,
+> > each sub-set of elements affected by the operation.
+
+With this principle, the algorithm becomes O(N^2)
+
+### Optimized
+
+Reading about posible optimizations,
+I found the possibility of summarizing the interior traversal with
+addition operations for each element in each row of operations,
+in only 2 constant operations, which represents the necessary values so that
+in a single final traversal, the sum values can be obtained "by drag".
+The algorithm is called "prefix sum."
+
+Some sources about "prefix sum"
+
+- <https://hmn.wiki/en/Prefix_sum>
+- <https://en.wikipedia.org/wiki/Prefix_sum>
+- <https://usaco.guide/silver/prefix-sums?lang=py>
+
+Some sources about implementation in:
+
+- [HackerRank Array Manipulation — beat the clock using Prefix Sum (JavaScript)](https://medium.com/@mlgerardvla/hackerrank-array-manipulation-beat-the-clock-using-prefix-sum-92471060035e)
+- [Hackerrank Discussions Forums: Array Manipulation](https://www.hackerrank.com/challenges/one-month-preparation-kit-crush/forum)

src/hackerrank/interview_preparation_kit/arrays/cruch_bruteforce.js

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+/**
+ * @link Problem definition [[docs/hackerrank/interview_preparation_kit/arrays/crush.md]]
+ * @see Solution Notes: [[docs/hackerrank/interview_preparation_kit/arrays/crush_optimized-solution-notes.md]]
+ */
+
+import { logger as console } from '../../../logger.js';
+
+export function arrayManipulation(n, queries) {
+  const LENGTH = n + 1;
+  const SURROGATE_VALUE = 0;
+  const result = Array(LENGTH).fill(SURROGATE_VALUE);
+  let maximum = 0;
+
+  queries.forEach((query) => {
+    const [aStart, bEnd, kValue] = query;
+    console.debug(`start -> ${result}`);
+
+    for (let i = aStart; i <= bEnd; i++) {
+      result[i] += kValue;
+      console.debug(`result -> ${result}`);
+    }
+  });
+
+  result.forEach((value) => {
+    maximum = Math.max(value, maximum);
+  });
+
+  return maximum;
+}
+
+export default { arrayManipulation };

src/hackerrank/interview_preparation_kit/arrays/cruch_bruteforce.test.js

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+import { describe, expect, it } from '@jest/globals';
+import { logger as console } from '../../../logger.js';
+
+import TEST_CASES from './cruch_testcases_test.json';
+
+import { arrayManipulation } from './cruch_bruteforce.js';
+
+describe('arrays: crush (bruteforce) small cases', () => {
+  it('arrayManipulation Test Cases', () => {
+    expect.assertions(3);
+
+    TEST_CASES.forEach((test) => {
+      const answer = arrayManipulation(test.n, test.queries);
+
+      console.debug(
+        `rotLeftOne(${test.n}, ${test.queries}) solution found: ${answer}`
+      );
+
+      expect(answer).toStrictEqual(test.expected);
+    });
+  });
+});

src/hackerrank/interview_preparation_kit/arrays/cruch_optimized.js

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+/**
+ * @link Problem definition [[docs/hackerrank/interview_preparation_kit/arrays/crush.md]]
+ */
+
+export function arrayManipulation(n, queries) {
+  // why adding 2?
+  //   first slot to adjust 1-based index and
+  //   last slot for storing accumSum result
+  const LENGTH = n + 2;
+  const INITIAL_VALUE = 0;
+  const result = Array(LENGTH).fill(INITIAL_VALUE);
+  let maximum = 0;
+
+  queries.forEach((query) => {
+    const [aStart, bEnd, kValue] = query;
+
+    result[aStart] += kValue;
+    result[bEnd + 1] -= kValue;
+  });
+
+  let accumSum = 0;
+
+  result.forEach((value) => {
+    accumSum += value;
+    maximum = Math.max(maximum, accumSum);
+  });
+
+  return maximum;
+}
+
+export default { arrayManipulation };

src/hackerrank/interview_preparation_kit/arrays/cruch_optimized.test.js

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+import { describe, expect, it } from '@jest/globals';
+import { logger as console } from '../../../logger.js';
+
+import TEST_CASES from './cruch_testcases_test.json';
+
+import { arrayManipulation } from './cruch_optimized.js';
+
+describe('arrays: crush (optimized)', () => {
+  it('arrayManipulation Test Cases', () => {
+    expect.assertions(3);
+
+    TEST_CASES.forEach((test) => {
+      const answer = arrayManipulation(test.n, test.queries);
+
+      console.debug(
+        `rotLeftOne(${test.n}, ${test.queries}) solution found: ${answer}`
+      );
+
+      expect(answer).toStrictEqual(test.expected);
+    });
+  });
+});

src/hackerrank/interview_preparation_kit/arrays/cruch_testcases_test.json

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