dmitry.twig.task.solution.js

/** *********************************
 *  return the contents of the array "arr" divided into "n" equally sized arrays
 *
 *  @param {number[]} arr - input array
 *  @param {integer} n - number of resulting arrays
 */
const groupArrayElements = (arr, n) => {
  if (n === 1) {
    return [arr]
  }
  const len = arr.length
  if (len < n) {
    // actually this is not necessarily an input error, depends on the requirements, but there are none
    throw new Error('WTF!')
  }

  // const chunk = Math.round(len / n) <-- doesn't work :(
  let chunk = Math.floor(len / n)
  if (chunk + (len % n) >= n) {
    ++chunk
  }

  const res = []
  for (let i = 0; i < n - 1; ++i) {
    res.push(arr.slice(i * chunk, (i + 1) * chunk))
  }
  res.push(arr.slice((n - 1) * chunk))
  return res
}

//  ---------------------------------
//  just so see how it works ...

// const getArray = len => Array.from({ length: len }, (_, i) => i + 1)

// console.log( groupArrayElements(getArray(6), 1) )
// console.log( groupArrayElements(getArray(6), 3) )
// console.log( groupArrayElements(getArray(6), 5) )
// console.log( groupArrayElements(getArray(6), 6) )
// console.log( groupArrayElements(getArray(3), 2) )

// console.log( groupArrayElements(getArray(11), 5) )
// console.log( groupArrayElements(getArray(12), 5) )
// console.log( groupArrayElements(getArray(13), 5) )
// console.log( groupArrayElements(getArray(14), 5) )
// console.log( groupArrayElements(getArray(15), 5) )
// console.log( groupArrayElements(getArray(16), 5) )

// with results like ...

// [[1, 2, 3, 4, 5, 6]]
// [[1, 2], [3, 4], [5, 6]]
// [[1], [2], [3], [4], [5, 6]]
// [[1], [2], [3], [4], [5], [6]]
// [[1, 2], [3]]
// [[1, 2], [3, 4], [5, 6], [7, 8], [9, 10, 11]]
// [[1, 2], [3, 4], [5, 6], [7, 8], [9, 10, 11, 12]]
// [[1, 2, 3], [4, 5, 6], [7, 8, 9], [10, 11, 12], [13]]
// [[1, 2, 3], [4, 5, 6], [7, 8, 9], [10, 11, 12], [13, 14]]
// [[1, 2, 3], [4, 5, 6], [7, 8, 9], [10, 11, 12], [13, 14, 15] ]
// [[1, 2, 3], [4, 5, 6], [7, 8, 9], [10, 11, 12], [13, 14, 15, 16]]

// here be tests ...
// for (let l = 3; l < 1000; ++l) {
//   for (let n = 2; n < l; ++n) {
//     // console.log(`l ${l}, n ${n}`)

//     const grouped = groupArrayElements(getArray(l), n)
//     assert.equal(grouped.length, n)

//     const lastItem = grouped[grouped.length - 1]
//     const prevLastItem = grouped[grouped.length - 2]
//     assert.ok(
//       grouped.length === 1 ||
//       lastItem.length <= prevLastItem.length ||
//       lastItem.length < n
//     )
//   }
// }