Data Structures: Array

hourglass.ts

const twoDimensionsArray = [
  [-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, -3, 0, 0],
  [ 0,  0, 1,  2, 4, 0],
]

const twoDimensionsArray2 = [
  [0, -4, -6, 0, -7, -6],
  [-1, -2, -6, -8, -3, -1],
  [-8, -4, -2, -8, -8, -6],
  [-3, -1, -2, -5, -7, -4],
  [-3, -5, -3, -6, -6, -6],
  [-3, -6, 0, -8, -6, -7],
]

function extractHourglasses(array2D) {
  const hourglasses = []
  
  for (let i = 0; i < array2D.length - 1; i++) {
    for (let j = 0; j < array2D[i].length; j++) {
      const [topA, topB, topC] = [
        array2D[i][j],
        array2D[i][j + 1],
        array2D[i][j + 2]
      ]
      
      const center = array2D[i + 1][j + 1]
      const [bottomA, bottomB, bottomC] = [
        array2D[i + 2] !== undefined && array2D[i + 2][j],
        array2D[i + 2] !== undefined && array2D[i + 2][j + 1],
        array2D[i + 2] !== undefined && array2D[i + 2][j + 2],
      ]
      
      if (
        topA !== undefined && topB !== undefined && topC !== undefined &&
        center !== undefined &&
        bottomA !== undefined && bottomB !== undefined && (bottomC !== undefined && bottomC !== false)
      ) {
        hourglasses.push([topA, topB, topC, center, bottomA, bottomB, bottomC])
      }
    }
  }
  
  return hourglasses
}

Math.max(...extractHourglasses(twoDimensionsArray)
  .map(hourglass => hourglass.reduce((acc, item) => acc + item, 0)))

reverse.ts

function reverse(target: array) {
  let reversed = [];

  for (var i = target.length - 1; i >= 0; i--) {
    reversed.push(target[i]);
  }

  return reversed;
}

const tostr = JSON.stringify

// Test Assertions
tostr(reverse([1, 4, 3, 2])) === '[2,3,4,1]';
tostr(reverse([-1, 2, 4, -3])) === '[-3,4,2,-1]';
tostr(reverse([4, 3, 2, 1])) === '[1,2,3,4]';