refactorPaths.py

# -----------------
# User Instructions
# 
# write a function, bsuccessors2 that takes a state as input
# and returns a dictionary of {state:action} pairs.
# 
# The new representation for a path should be a list of 
# [state, (action, total time), state, ... , ], though this 
# function will just return {state:action} pairs and will
# ignore total time. 
#
# The previous bsuccessors function is included for your reference.

def bsuccessors2(state):
    """Return a dict of {state:action} pairs. A state is a
    (here, there) tuple, where here and there are frozensets
    of people (indicated by their travel times) and/or the light."""
    here, there = state
    if 'light' in here:
        return dict(((here  - frozenset([a,b, 'light']),
                      there | frozenset([a, b, 'light'])),
                     (a, b, '->'))
                    for a in here if a is not 'light'
                    for b in here if b is not 'light')
    else:
        return dict(( (here  | frozenset([a,b, 'light']),
                      there - frozenset([a, b, 'light']) ),
                     (a, b, '<-'))
                    for a in there if a is not 'light'
                    for b in there if b is not 'light')  

def bsuccessors(state):
    """Return a dict of {state:action} pairs.  A state is a (here, there, t) tuple,
    where here and there are frozensets of people (indicated by their times) and/or
    the light, and t is a number indicating the elapsed time."""
    here, there, t = state
    if 'light' in here:
        return dict(((here  - frozenset([a,b, 'light']),
                      there | frozenset([a, b, 'light']),
                      t + max(a, b)),
                     (a, b, '->'))
                    for a in here if a is not 'light'
                    for b in here if b is not 'light')
    else:
        return dict(((here  | frozenset([a,b, 'light']),
                      there - frozenset([a, b, 'light']),
                      t + max(a, b)),
                     (a, b, '<-'))
                    for a in there if a is not 'light'
                    for b in there if b is not 'light')  


def test():
    here1 = frozenset([1, 'light']) 
    there1 = frozenset([])

    here2 = frozenset([1, 2, 'light'])
    there2 = frozenset([3])
    
    assert bsuccessors2((here1, there1)) == {
            (frozenset([]), frozenset([1, 'light'])): (1, 1, '->')}
    assert bsuccessors2((here2, there2)) == {
            (frozenset([1]), frozenset(['light', 2, 3])): (2, 2, '->'), 
            (frozenset([2]), frozenset([1, 3, 'light'])): (1, 1, '->'), 
            (frozenset([]), frozenset([1, 2, 3, 'light'])): (2, 1, '->')}
    return 'tests pass'
print ( test() )