MockInterviewPractice8.js

/**
 * 
 Introduction:

You've built an inflight entertainment system with on-demand movie streaming.
 
Users on longer flights like to start a second movie right when their first one ends, but they complain that the plane usually lands before they can see the ending. So you're building a feature for choosing two movies whose total runtimes will equal the exact flight length.


Problem: 

  
Write a function that takes an integer flightLength (in minutes) and an array of integers movieLengths (in minutes) and returns a boolean indicating whether there are two numbers in movieLengths whose sum equals flightLength.

When building your function:
 
Assume your users will watch exactly two movies
Don't make your users watch the same movie twice
Optimize for runtime over memory

*/

function canTwoMoviesFillFlight(movieLengths, flightLength) {
  // const moviesMap = {};
  const movieSet = new Set();
  for (let i = 0; i < movieLengths.length; i++) {
    let isMatch = flightLength - movieLengths[i];
    if (movieSet.has(isMatch)) {
      return true;
    }
    // moviesMap[movieLengths[i]] = true
    movieSet.add(movieLengths[i]);
  }
  return false;
}

// Tests
function assertEquals(a, b, desc) {
  if (a === b) {
    console.log(`${desc} ... PASS`);
  } else {
    console.log(`${desc} ... FAIL: ${a} != ${b}`);
  }
}

let desc = 'short flight';
let actual = canTwoMoviesFillFlight([2, 4], 1);
let expected = false;
assertEquals(actual, expected, desc);

desc = 'long flight';
actual = canTwoMoviesFillFlight([2, 4], 6);
expected = true;
assertEquals(actual, expected, desc);

desc = 'one movie half flight length';
actual = canTwoMoviesFillFlight([3, 8], 6);
expected = false;
assertEquals(actual, expected, desc);

desc = 'two movies half flight length';
actual = canTwoMoviesFillFlight([3, 8, 3], 6);
expected = true;
assertEquals(actual, expected, desc);

desc = 'lots of possible pairs';
actual = canTwoMoviesFillFlight([1, 2, 3, 4, 5, 6], 7);
expected = true;
assertEquals(actual, expected, desc);

desc = 'not using first movie';
actual = canTwoMoviesFillFlight([4, 3, 2], 5);
expected = true;
assertEquals(actual, expected, desc);

desc = 'only one movie';
actual = canTwoMoviesFillFlight([6], 6);
expected = false;
assertEquals(actual, expected, desc);

desc = 'no movies';
actual = canTwoMoviesFillFlight([], 2);
expected = false;
assertEquals(actual, expected, desc);