trransformArray

trransformArray

by Alexey

JavaScript

function trransformArray(arr) {
  let arr2 = [];
  let from = 0;
  let to = 0;
  for (let i = 1; i < arr.length; i++) {
    if (arr[i] === arr[i - 1] + 1) {
      to = i;
    } else {
      if (from === to) {
        arr2.push(arr[from]);
      } else {
        arr2.push(arr[from] + '-' + arr[to]);
      }
      from = i;
      to = from;
    }
  }

  if (from === to) {
    arr2.push(arr[from]);
  } else {
    arr2.push(arr[from] + '-' + arr[to]);
  }
  return (arr2.join(', '));
}

let arr = [ -10,-9,-8,-5,-3,-2,0,1,2,3,4,5,8,9,11,13,15,18,22,25,28,29,30];

console.log(trransformArray(arr));