Take a Ten Minute Walk (JavaScript)

My 8-hour coding days at Flatiron are a thing of the past (quietly sobbing, brb), but, as with learning any new language, practice or lose it.

Practice it is! I dipped into Codewars again today. I was rusty, but here goes.

Today's challenge (JavaScript):

You live in the city of Cartesia where all roads are laid out in a perfect
grid. You arrived 10 minutes too early to an appointment, so you decided
to take the opportunity to go for a short walk. 

The city provides its citizens with a Walk Generating App on their phones
-- every time you press the button it sends you an array of one-letter
strings representing directions to walk (eg. ['n', 's', 'w', 'e']). 

You always walk only a single block in a direction and you know it takes
you 1 minute to traverse one city block, so create a function that will
return true if the walk the app gives you will take you exactly 10
minutes (you don't want to be early or late!) and will, of course, return
you to your starting point. Return false otherwise.

Note: you will always receive a valid array containing a random assortment
of direction letters ('n', 's', 'e', or 'w' only). It will never give you
an empty array (that's not a walk, that's standing still!).

It's often hard to dive straight into code, so I pseudo-code instead:

// 1 block = 1 minute
// if walk = 10 minutes, true
// otherwise false
// must return to starting point
// if paths start with 0 (set equal to 0) we can increment or decrement
// then, if a path ends again with 0, we know it can return true

The idea is forming, now let's get closer to code with the details:

// ns (north-south) should equal 0 
// we (west-east) should equal 0 

// if the direction is north, north-south add 1 - leaving
// if the direction is south, north-south subtract 1 - coming back
// if the direction is west, west-east add 1 - leaving
// if the direction is east, west-east subtract 1 - coming back

// if the length of the walk is equal to 10 and ns is 0 and we is 0, return the walk length, otherwise return false

Format is coming together, let's build out that function:

function isValidWalk(walk) {
  let ns = 0, we = 0; 
    for (let dir of walk) { 
      if (dir == 'n') ns += 1; 
      if (dir == 's') ns -= 1; 
      if (dir == 'w') we += 1; 
      if (dir == 'e') we -= 1; 
    } 

    return walk.length == 10 && ns === 0 && we === 0; 
}

The thing I love after submitting a solution is seeing what other people submitted. Here were other clever solutions!

Clever Solution 1 (and most popular):

function isValidWalk(walk) {
  var dx = 0
  var dy = 0
  var dt = walk.length

  for (var i = 0; i < walk.length; i++) {
    switch (walk[i]) {
      case 'n': dy--; break
      case 's': dy++; break
      case 'w': dx--; break
      case 'e': dx++; break
    }
  }

  return dt === 10 && dx === 0 && dy === 0
}

Clever Solution 2:

function isValidWalk(walk) {
  function count(val) {
    return walk.filter(function(a){return a==val;}).length;
  }
  return walk.length==10 && count('n')==count('s') && count('w')==count('e');
}

Clever Solution 3:

function isValidWalk(walk) {
  const north = walk.filter(item => { return item === "n" }).length;
  const south = walk.filter(item => { return item === "s" }).length;
  const east = walk.filter(item => { return item === "e" }).length;
  const west = walk.filter(item => { return item === "w" }).length;

  return walk.length === 10 && north === south && east === west;
}

After too many hours (yes, that's plural) of working through this, it's time to go on a real 10-minute walk.

Thanks so much for reading, and if you also worked through this but came up with a different solution, share it in the comments below!

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Take a Ten Minute Walk (JavaScript)

Anna Wijetunga

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