Solution to hallway challenge from "Fake coding interview with Dan Abramov"

solution.js

// From: https://youtu.be/-w-P4u0x8ig?t=3075

function countMeetings(hallway) {
  // Let's go over the hallway from left to right and keep track of how many
  // people are moving right behind us at that point. Each time we encounter
  // someone moving left, we know they will meet everyone who is moving right
  // behind us at that point, so we add that number to the meetings count.
  let peopleMovingRightBehindUs = 0;
  let meetings = 0;
  for (const char of hallway) {
    if (char === '>') {
      peopleMovingRightBehindUs += 1;
    } else if (char === '<') {
      meetings += peopleMovingRightBehindUs;
    } else if (char === '-') {
      // Do nothing
    } else {
      throw `Unexpected character in input`;
    }
  }
  return meetings;
}

const testCases = [
  [`<---->---<---<-->`, 4],
  [`------`, 0],
  [`>>>>>>>>>>>>>>>>>>>>>----<->`, 42],
  [`<<----<>---<`, 2],
  [`>`, 0],
];

testCases.forEach(([hallway, correctResult], index) => {
  const salutes = countMeetings(hallway) * 2;
  console.log({ index, expected: correctResult, got: salutes });
});

// Output:
// {index: 0, expected: 4, got: 4}
// {index: 1, expected: 0, got: 0}
// {index: 2, expected: 42, got: 42}
// {index: 3, expected: 2, got: 2}
// {index: 4, expected: 0, got: 0}