Hacker Rank - DS - 2D Arrays - JavaScript

index.js

'use strict'

const input = [
  [-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]
]

const buildVectorsForSquareMatrix = (matrixSize) => {
  const vectors = []

  for (let x = 0; x < matrixSize; x++) {
    for (let y = 0; y < matrixSize; y++) {
      vectors.push([x, y])
    }
  }

  return vectors
}

const maybeHourglassFromStartingVector = ([x, y], matrix, matrixSize) => {
  // we're too close to the bottom edge, the hourglass won't fit
  if ((y + 3) > matrixSize) {
    return null
  }

  // we're too close to the right edge, the hourglass won't fit
  if ((x + 3) > matrixSize) {
    return null
  }

  //    x0 x1 x2
  // y0 -9 -9 -9
  // y1    -9
  // y2 -9 -9 -9
  return [
    matrix[y].slice(x, x + 3),
    [ matrix[y + 1][x + 1] ],
    matrix[y + 2].slice(x, x + 3)
  ]
}

const sumMatrix = (matrix) => {
  return matrix
    .flat()
    .reduce((a, b) => a + b)
}

const getHourglassWithHighestSum = (matrix) => {
  const matrixSize = matrix.length

  const hourglassSums = buildVectorsForSquareMatrix(matrixSize)
    .map((startingVector) => maybeHourglassFromStartingVector(startingVector, matrix, matrixSize))
    .filter((hourglass) => hourglass !== null)
    .map(hourglass => sumMatrix(hourglass))

  return Math.max(...hourglassSums)
}

console.log('max', getHourglassWithHighestSum(input))
// 28