Solution to http://adventofcode.com/2016/day/2 using reduce and accumulate

d2p1.py

#!/usr/bin/env python3

# Solution to http://adventofcode.com/2016/day/2 part 1
# using reduce and accumulate for awesome functional programing style points
# Mark Jenkins <mark@markjenkins.ca>

from sys import stdin

from functools import reduce
from itertools import chain, accumulate, islice

START_LOCATION = "5"
ROW_SIZE = 3

FIRST_NUM = 1
LAST_NUM = 9

def same_row(num, num_next):
    # integer arithmatic, shifting over to a 0-8 scale means that
    # assert(0//3 == 1//3 == 2//3)
    # assert(3//3 == 4//3 == 5//3)
    # assert(6//3 == 7//3 == 8//3)
    if not (FIRST_NUM<=num<=LAST_NUM):
        return False
    else:
        return (num-1)//ROW_SIZE == (num_next-1)//ROW_SIZE

def move_graph_entry(num):
    return {
        "U": num if num-ROW_SIZE < FIRST_NUM else num-ROW_SIZE,
        "D": num if num+ROW_SIZE > LAST_NUM else num+ROW_SIZE,
        "R": num if not same_row(num, num+1) else num+1,
        "L": num if not same_row(num, num-1) else num-1,
        }

def stringified_move_graph_entry(int_move_graph):
    return { key: str(val) for key,val in int_move_graph.items() }

MOVE_GRAPH = {
    str(num): stringified_move_graph_entry(move_graph_entry(num))
    for num in range(FIRST_NUM, LAST_NUM+1)
}

def reduce_location_and_line_to_location(location, line):
    return reduce(
        lambda loc, character: MOVE_GRAPH[loc][character],
        line, # sequence of characters
        location)

location = START_LOCATION

# finish this the imperative way
# for line in stdin:
#      location = reduce_location_and_line_to_location(location, line.strip() )
#      print(location, end='')
# print()

# or, finish this with accumulate() feeding ''.join(), because we can
print( ''.join( islice( accumulate( 
    chain( (START_LOCATION,),
           (line.strip() for line in stdin) ),
    lambda loc, line: reduce_location_and_line_to_location(loc, line) ),
                        1, None
                        ) # islice
) # join
) # print

d2p2.py

#!/usr/bin/env python3

# Solution to http://adventofcode.com/2016/day/2 part 2
# Simply patch my solution to part 1 with a different MOVE_GRAPH
# Mark Jenkins <mark@markjenkins.ca>

from sys import stdin

from functools import reduce
from itertools import chain, accumulate, islice

START_LOCATION = "5"
ROW_SIZE = 3

FIRST_NUM = 1
LAST_NUM = 9

def same_row(num, num_next):
    # integer arithmatic, shifting over to a 0-8 scale means that
    # assert(0//3 == 1//3 == 2//3)
    # assert(3//3 == 4//3 == 5//3)
    # assert(6//3 == 7//3 == 8//3)
    if not (FIRST_NUM<=num<=LAST_NUM):
        return False
    else:
        return (num-1)//ROW_SIZE == (num_next-1)//ROW_SIZE

def move_graph_entry(num):
    return {
        "U": num if num-ROW_SIZE < FIRST_NUM else num-ROW_SIZE,
        "D": num if num+ROW_SIZE > LAST_NUM else num+ROW_SIZE,
        "R": num if not same_row(num, num+1) else num+1,
        "L": num if not same_row(num, num-1) else num-1,
        }

def stringified_move_graph_entry(int_move_graph):
    return { key: str(val) for key,val in int_move_graph.items() }

MOVE_GRAPH_OLD = {
    str(num): stringified_move_graph_entry(move_graph_entry(num))
    for num in range(FIRST_NUM, LAST_NUM+1)
}

MOVE_GRAPH_PATCH = {
    str(num): str(num+1)
    for num in range(FIRST_NUM, 3+1)
    }
MOVE_GRAPH_PATCH.update(
    { str(num): str(num+2)
      for num in range(4,6+1)
    }
    )
MOVE_GRAPH_PATCH.update(
    { num: new_let
    for num, new_let in zip( "789", "ABC")
        }
    )

MOVE_GRAPH = {
    MOVE_GRAPH_PATCH[key]: {direction: MOVE_GRAPH_PATCH[destination]
                           for direction, destination in value.items()
                       }
    for key, value in MOVE_GRAPH_OLD.items()
    }

MOVE_GRAPH.update(
    { '1': {'U':'1', 'R':'1', 'D':'3', 'L': '1'},
      '9': {'U':'9', 'R':'9', 'D':'9', 'L': '8'},
      'D': {'U':'B', 'R':'D', 'D':'D', 'L': 'D'},
      '5': {'U':'5', 'R':'6', 'D':'5', 'L': '5'},
    } )
MOVE_GRAPH['3']['U'] = '1'
MOVE_GRAPH['8']['R'] = '9'
MOVE_GRAPH['B']['D'] = 'D'
MOVE_GRAPH['6']['L'] = '5'


def reduce_location_and_line_to_location(location, line):
    return reduce(
        lambda loc, character: MOVE_GRAPH[loc][character],
        line, # sequence of characters
        location)

location = START_LOCATION

# finish this the imperative way
# for line in stdin:
#      location = reduce_location_and_line_to_location(location, line.strip() )
#      print(location, end='')
# print()

# or, finish this with accumulate() feeding ''.join(), because we can
print( ''.join( islice( accumulate( 
    chain( (START_LOCATION,),
           (line.strip() for line in stdin) ),
    lambda loc, line: reduce_location_and_line_to_location(loc, line) ),
                        1, None
                        ) # islice
) # join
) # print