Once upon a time, on a way through the old wild west,…

… a man was given directions to go from one point to another. The directions were "NORTH", "SOUTH", "WEST", "EAST". Clearly "NORTH" and "SOUTH" are opposite, "WEST" and "EAST" too. Going to one direction and coming back the opposite direction is a needless effort. Since this is the wild west, with dreadfull weather and not much water, it's important to save yourself some energy, otherwise you might die of thirst!

How I crossed the desert the smart way.

The directions given to the man are, for example, the following:

["NORTH", "SOUTH", "SOUTH", "EAST", "WEST", "NORTH", "WEST"].
or

{ "NORTH", "SOUTH", "SOUTH", "EAST", "WEST", "NORTH", "WEST" };
or (haskell)

[North, South, South, East, West, North, West]
You can immediatly see that going "NORTH" and then "SOUTH" is not reasonable, better stay to the same place! So the task is to give to the man a simplified version of the plan. A better plan in this case is simply:

["WEST"]
or

{ "WEST" }
or (haskell)

[West]
or (rust)

[WEST];
Other examples:

In ["NORTH", "SOUTH", "EAST", "WEST"], the direction "NORTH" + "SOUTH" is going north and coming back right away. What a waste of time! Better to do nothing.

The path becomes ["EAST", "WEST"], now "EAST" and "WEST" annihilate each other, therefore, the final result is [] (nil in Clojure).

In ["NORTH", "EAST", "WEST", "SOUTH", "WEST", "WEST"], "NORTH" and "SOUTH" are not directly opposite but they become directly opposite after the reduction of "EAST" and "WEST" so the whole path is reducible to ["WEST", "WEST"].

Task

Write a function dirReduc which will take an array of strings and returns an array of strings with the needless directions removed (W<->E or S<->N side by side).

The Haskell version takes a list of directions with data Direction = North | East | West | South. The Clojure version returns nil when the path is reduced to nothing. The Rust version takes a slice of enum Direction {NORTH, SOUTH, EAST, WEST}.

Examples

dirReduc({"NORTH", "SOUTH", "SOUTH", "EAST", "WEST", "NORTH", "WEST"}) => {"WEST"}
dirReduc({"NORTH", "SOUTH", "SOUTH", "EAST", "WEST", "NORTH"}) => {}
See more examples in "Example Tests"

Note

Not all paths can be made simpler. The path ["NORTH", "WEST", "SOUTH", "EAST"] is not reducible. "NORTH" and "WEST", "WEST" and "SOUTH", "SOUTH" and "EAST" are not directly opposite of each other and can't become such. Hence the result path is itself : ["NORTH", "WEST", "SOUTH", "EAST"].

Using JavaScript

function dirReduc(arr){
var string = arr.join( " " );
var wrongMatch = /NORTHSOUTH|SOUTHNORTH|EASTWEST|WESTEAST/;
while(wrongMatch.test(string)) {
string = string.replace(wrongMatch, '');
}
return string.match(/NORTH|SOUTH|EAST|WEST/) || [];
}

Isnt this a case of just removing pairs of opposing directions till you are left with one or none...?

nsimageorge:
Using JavaScript

function dirReduc(arr){
var string = arr.join( " " );
var wrongMatch = /NORTHSOUTH|SOUTHNORTH|EASTWEST|WESTEAST/;
while(wrongMatch.test(string)) {
string = string.replace(wrongMatch, '');
}
return string.match(/NORTH|SOUTH|EAST|WEST/) || [];
}

Your code didnt pass it... sorry

frankg1:


Your code didnt pass it... sorry

https://codepen.io/nsimageorge/pen/VMpeVB

This is my solution on code pen...
How did it not pass??

nsimageorge:


https://codepen.io/nsimageorge/pen/VMpeVB

This is my solution on code pen...
How did it not pass??

run it here https://www.codewars.com/kata/directions-reduction/train/javascript.

that is where i got the question from

frankg1:


run it here https://www.codewars.com/kata/directions-reduction/train/javascript.

that is where i got the question from

Okay, I see my mistake

function dirReduc(arr){
var string = arr.join( '' );
var wrongMatch = /NORTHSOUTH|SOUTHNORTH|EASTWEST|WESTEAST/;
while(wrongMatch.test(string)) {
string = string.replace(wrongMatch, '');
}
return string.match(/NORTH|SOUTH|EAST|WEST/g) || [];
}

Not clear what to do.

Do we . Take a dir.. like go north, then we can't got north again?

orimion and Haskell are 5 and 6

def dirReduc(l):
cor = ['NORTH','SOUTH','WEST','EAST']
i = 0
while i < len(l)-1:
if l[i] == cor[0] and l[i+1] == cor[1] or l[i] == cor[1] and l[i+1] == cor[0]:
del(l[i])
del(l[i])
i = 0
elif l[i] == cor[2] and l[i+1] == cor[3] or l[i] == cor[3] and l[i+1] == cor[2]:
del(l[i])
del(l[i])
i = 0
else:
i += 1
return l

orimion:
Haskell

dirReduce :: [Direction] -> [Direction]
dirReduce xs =
  case reduce 0 [] xs of
    (0, ds) -> reverse ds
    (_, ds) -> dirReduce $ reverse ds

reduce :: Int -> [Direction] -> [Direction] -> (Int, [Direction])
reduce t acc [] = (t, acc)
reduce t acc (North:South:ds) = reduce (t + 1) acc ds
reduce t acc (South:North:ds) = reduce (t + 1) acc ds
reduce t acc (West:East:ds) = reduce (t + 1) acc ds
reduce t acc (East:West:ds) = reduce (t + 1) acc ds
reduce t acc (d:ds) = reduce t (d : acc) ds

i dont understand this haskell one bit... but it works though

deedat205:
orimion and Haskell are 5 and 6

def dirReduc(l):
	cor = ['NORTH','SOUTH','WEST','EAST']
	i = 0
	while i < len(l)-1:
		if l[i] == cor[0] and l[i+1] == cor[1] or l[i] == cor[1] and l[i+1] == cor[0]:
			del(l[i])
			del(l[i])
			i = 0
		elif l[i] == cor[2] and l[i+1] == cor[3] or l[i] == cor[3] and l[i+1] == cor[2]:
			del(l[i])
			del(l[i])
			i = 0
		else:
			i += 1
	return l

don't you just love how it reads

frankg1:



i dont understand this haskell one bit... but it works though

http://learnyouahaskell.com it'll challenge everything you know about programming