Source

Source: Advent of Code 2016, Day 1: No Time for a Taxicab

Description

Given an array p of strings representing instructions, each in the format Ln or Rn where n is an integer, return the taxicab distance or “Manhattan distance” in blocks from point 0, 0 on a street grid to the point reached by following the sequence of instructions.

For each instruction, turn either left (L) or right (R) 90 degrees, then walk n blocks forward.

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['R2', 'L3'] ⟹ 5
['R5', 'L5', 'R5', 'R3'] ⟹ 12
['R2', 'R2', 'R2'] ⟹ 2

My solution

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nsew = {
    'north': {
        'R': 'east',
        'L': 'west', 
        'walk': lambda x, y, steps: (x, y + steps)
    },
    'south': {
        'R': 'west', 
        'L': 'east',
        'walk': lambda x, y, steps: (x, y - steps)
    },
    'east': {
        'R': 'south',
        'L': 'north',
        'walk': lambda x, y, steps: (x + steps, y)
    },
    'west': {
        'R': 'north',
        'L': 'south',
        'walk': lambda x, y, steps: (x - steps, y)
    }
}

        
def taxidistance(path, x=0, y=0, direc='north'):
    x0, y0 = x, y
    for turn in path:
        rl, steps = turn[0], int(turn[1])
        direc = nsew[direc][rl]           # update direction faced
        walk = nsew[direc]['walk']        # get walk function
        x, y = walk(x, y, steps)          # walk in current direction
    return abs(x0 - x) + abs(y0 - y)      # via formula

Tests

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import pytest
from taxidistance import *


def test_taxidistance():
    """Should calculate taxi distance correctly."""
    assert taxidistance(['R2', 'L3']) == 5
    assert taxidistance(['R5', 'L5', 'R5', 'R3']) == 12
    assert taxidistance(['R2', 'R2', 'R2']) == 2