Check-the-exam.js

/*
  The first input array is the key to the correct answers to an exam, like ["a", "a", "b", "d"]. The second one contains a student's submitted answers.

  The two arrays are not empty and are the same length. Return the score for this array of answers, giving +4 for each correct answer, -1 for each incorrect answer, and +0 for each blank answer, represented as an empty string (in C the space character is used).

  If the score < 0, return 0.

  For example:

  checkExam(["a", "a", "b", "b"], ["a", "c", "b", "d"]) → 6
  checkExam(["a", "a", "c", "b"], ["a", "a", "b",  ""]) → 7
  checkExam(["a", "a", "b", "c"], ["a", "a", "b", "c"]) → 16
  checkExam(["b", "c", "b", "a"], ["",  "a", "a", "c"]) → 0
*/

// Answer:

function checkExam(answers, guesses) {
  return Math.max(
    0,
    guesses.reduce((acc, curr, i) => {
      switch (curr) {
        case answers[i]:
          return acc + 4;
        case "":
          return acc;
        default:
          return acc - 1;
      }
    }, 0)
  );
}

// BigO: O(n)