"The successful warrior is the average man, with laser-like focus." - Bruce Lee

cassidoo Challenge 10-27

function missingInts(arr) {
  if (arr.length < 2) return [];

  const missingNums = [];
  const set = new Set(arr);
  
  for (let i = 1; i < arr[arr.length - 1]; i++) {
    if (!set.has(i)) missingNums.push(i);
  }
  
  return missingNums;
}

missingInts([1, 3, 3, 3, 5, 6]);
missingInts([1, 2, 3, 4, 4, 7, 7]);