Function isOneOrLessAway

strings/one-away.js:20–44

(str1, str2)

 * @return {boolean}      True if strings are 0 or 1 edit apart, otherwise false
 */
export function isOneOrLessAway(str1, str2) {
  // if lengths differ by more than 1 then can't be true
  if (Math.abs(str1.length - str2.length) > 1) {
    return false;
  }

  let isEdited = false;
  for (let i = 0, j = 0; i < str1.length && j < str2.length; ++i, ++j) {
    if (str1[i] !== str2[j]) {
      if (isEdited) {
        // second edit
        return false;
      }

      if (str1.length > str2.length) {
        --j; // decrease j, we are deleting char from str1
      } else if (str1.length < str2.length) {
        --i; // decrease i, we are deleting char from str2
      }
      isEdited = true;
    }
  }

  return true;
}

// Time O(n + m)
// Space O(max(n + m))