30-seconds-of-code/snippets/isSorted.md

title, tags

title	tags
isSorted	array,intermediate

Returns 1 if an array of numbers is sorted in ascending order, -1 if it is sorted in descending order or 0 if it is not sorted.

• Calculate the ordering direction for every pair of adjacent array elements.
• Return 0 if the direction changes or the direction sign if the last element is reached.

const isSorted = arr => {
  let direction = 0;
  for (let i = 1; i < arr.length; i++) {
    if (!direction) direction = arr[i] - arr[i - 1];
    else if ((arr[i] - arr[i - 1]) * direction < 0) return 0;
  }
  return Math.sign(direction);
};

isSorted([0, 1, 2, 2]); // 1
isSorted([4, 3, 2]); // -1
isSorted([4, 3, 5]); // 0
isSorted([4]); // 0