[Hacker Rank] Interview Preparation Kit: Array: 2D Array - DS. Solved ✅.

Author: Gonzalo Diaz

docs/hackerrank/interview_preparation_kit/arrays/2d_array.md

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+# [Arrays: 2D Array - DS](https://www.hackerrank.com/challenges/2d-array)
+
+- Difficulty:  ` #easy `
+- Category: ` #ProblemSolvingBasic `
+
+Given a 6 × 6  2D Array, `arr`:
+
+```text
+1 1 1 0 0 0
+0 1 0 0 0 0
+1 1 1 0 0 0
+0 0 0 0 0 0
+0 0 0 0 0 0
+0 0 0 0 0 0
+```
+
+An hourglass in `A` is a subset of values with indices falling in this pattern
+ in `arr`'s graphical representation:
+
+```text
+a b c
+  d
+e f g
+```
+
+There are `16` hourglasses in `arr`.
+An hourglass sum is the sum of an hourglass' values.
+Calculate the hourglass sum for every hourglass in `arr`,
+then print the maximum hourglass sum. The array will always be 6 × 6.
+
+## Example
+
+arr =
+
+```text
+-9 -9 -9  1 1 1
+ 0 -9  0  4 3 2
+-9 -9 -9  1 2 3
+ 0  0  8  6 6 0
+ 0  0  0 -2 0 0
+ 0  0  1  2 4 0
+```
+
+The `16` hourglass sums are:
+
+```text
+-63, -34, -9, 12,
+-10,   0, 28, 23,
+-27, -11, -2, 10,
+  9,  17, 25, 18
+```
+
+The highest hourglass sum is `26` from the hourglass beginning
+at row `1`, column `2`:
+
+```text
+0 4 3
+  1
+8 6 6
+````
+
+**Note**: If you have already solved the Java domain's Java 2D Array challenge,
+you may wish to skip this challenge.
+
+## Function Description
+
+Complete the function hourglassSum in the editor below.
+
+hourglassSum has the following parameter(s):
+
+- `int arr[6][6]`: an array of integers
+
+## Returns
+
+- int: the maximum hourglass sum
+
+## Input Format
+
+Each of the `6` lines of inputs `arr[i]` contains space-separated integers `arr[i][j]`.
+
+## Constraints
+
+- $9 \leq arr[i][j] \leq 9$
+- $0 \leq i, j \leq 5$
+
+## Output Format
+
+Print the largest (maximum) hourglass sum found in `arr`.
+
+## Sample Input
+
+```text
+1 1 1 0 0 0
+0 1 0 0 0 0
+1 1 1 0 0 0
+0 0 2 4 4 0
+0 0 0 2 0 0
+0 0 1 2 4 0
+```
+
+## Sample Output
+
+```text
+19
+```
+
+## Explanation
+
+`arr` contains the following hourglasses:
+
+```text
+111 110 100 000
+ 1   0   0   0
+111 110 100 000
+
+010 100 000 000
+ 0   1   0   0
+002 024 244 440
+
+111 110 100 000
+ 0   2   4   4
+000 002 020 200
+
+002 024 244 440
+ 0   0   2   0
+001 012 124 240
+```
+
+The hourglass with the maximum sum (`19`) is:
+
+```text
+2 4 4
+  2
+1 2 4
+```

src/hackerrank/interview_preparation_kit/arrays/2d_array.js

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+/**
+ * @link Problem definition [[docs/hackerrank/interview_preparation_kit/arrays/2d_array.md]]
+ */
+
+export function gethourGlass(
+  arr,
+  positionX,
+  positionY
+) {
+  const result = [];
+
+  // top
+  result.push(arr[positionX - 1][positionY - 1]);
+  result.push(arr[positionX - 1][positionY]);
+  result.push(arr[positionX - 1][positionY + 1]);
+  // middle
+  result.push(arr[positionX][positionY]);
+  // bottom
+  result.push(arr[positionX + 1][positionY - 1]);
+  result.push(arr[positionX + 1][positionY]);
+  result.push(arr[positionX + 1][positionY + 1]);
+  return result;
+}
+
+export function hourglassSum(arr) {
+  let matrixSize = 0;
+
+  if (arr?.[0]) {
+    matrixSize = arr.length;
+  }
+
+  const matrixStartIndex = 1;
+  const matrixStopIndex = matrixSize - 2;
+
+  console.debug(`matrix size ${matrixSize}`);
+
+  let maxHourglassSum = null;
+
+  // recorrido
+  for (let i = matrixStartIndex; i <= matrixStopIndex; i++) {
+    for (let j = matrixStartIndex; j <= matrixStopIndex; j++) {
+      // hourglass centers
+      console.debug(`posicion (${i},${j}): ${arr[i][j]}`);
+
+      const houglassValues = gethourGlass(arr, i, j);
+
+      const thisHourglassSum = houglassValues.reduce(
+        (a, b) => a + b,
+        0
+      );
+
+      console.debug(houglassValues, `thisHourglassSum: ${thisHourglassSum}`);
+
+      if (
+        maxHourglassSum === undefined ||
+        maxHourglassSum === null ||
+        thisHourglassSum > maxHourglassSum
+      ) {
+        maxHourglassSum = thisHourglassSum;
+      }
+    }
+  }
+
+  return maxHourglassSum;
+}
+
+export default { hourglassSum };

src/hackerrank/interview_preparation_kit/arrays/2d_array.test.js

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+import { describe, expect, it } from '@jest/globals';
+import { logger as console } from '../../../logger.js';
+
+import { hourglassSum } from './2d_array.js';
+import TEST_CASES from './2d_array.testcases_test.json';
+
+describe('arrays: 2d Array hourglassSum', () => {
+  it('hourglassSum Test Cases', () => {
+    expect.assertions(1);
+
+    TEST_CASES.forEach((test) => {
+      const answer = hourglassSum(test.input);
+
+      console.debug(
+        `gethourGlass(${test.input.toString()}) solution found: ${answer}`
+      );
+
+      expect(answer).toStrictEqual(test.expected);
+    });
+  });
+});

src/hackerrank/interview_preparation_kit/arrays/2d_array.testcases_test.json

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+[
+  {
+    "title": "Sample Test Case 0",
+    "input": [
+      [1, 1, 1, 0, 0, 0],
+      [0, 1, 0, 0, 0, 0],
+      [1, 1, 1, 0, 0, 0],
+      [0, 0, 2, 4, 4, 0],
+      [0, 0, 0, 2, 0, 0],
+      [0, 0, 1, 2, 4, 0]
+    ],
+    "expected": 19
+  }
+]