Directions Reduction.py

# Once upon a time, on a way through the old wild mountainous 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 right away is a needless effort. Since this is the wild west, with dreadful weather and not much water, it's important to save yourself some energy, otherwise you might die of thirst!

# How I crossed a mountainous desert the smart way.
# The directions given to the man are, for example, the following (depending on the language):

# ["NORTH", "SOUTH", "SOUTH", "EAST", "WEST", "NORTH", "WEST"].
# or
# { "NORTH", "SOUTH", "SOUTH", "EAST", "WEST", "NORTH", "WEST" };
# or
# [North, South, South, East, West, North, West]
# You can immediately see that going "NORTH" and immediately "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
# [West]
# Other examples:
# In ["NORTH", "SOUTH", "EAST", "WEST"], the direction "NORTH" + "SOUTH" is going north and coming back right away.

# 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, East, West, South}.
# See more examples in "Sample Tests:"
# Notes
# 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"].
# if you want to translate, please ask before translating.


def dir_reduc(arr):
    directions = []
    for direction in arr:
        if directions:
            last_direction = directions[-1]
            if (direction == 'NORTH' and last_direction == 'SOUTH') or \
               (direction == 'SOUTH' and last_direction == 'NORTH') or \
               (direction == 'WEST' and last_direction == 'EAST') or \
               (direction == 'EAST' and last_direction == 'WEST'):
                directions.pop()  # Cancel out the last direction
            else:
                directions.append(direction)
        else:
            directions.append(direction)
    
    return directions