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Pearls in the box - recursion solution in Clear category for Pearls in the Box by narimiran
def prob(white, black, step):
white_prob = white / (white+black)
black_prob = 1 - white_prob
if step == 1:
return white_prob
else:
pick_white = white_prob * prob(white-1, black+1, step-1)
pick_black = black_prob * prob(white+1, black-1, step-1)
return pick_white + pick_black
def checkio(marbles, step):
return round(prob(marbles.count('w'), marbles.count('b'), step), 2)
# These "asserts" using only for self-checking and not necessary for auto-testing
if __name__ == '__main__':
assert checkio('bbw', 3) == 0.48, "1st example"
assert checkio('wwb', 3) == 0.52, "2nd example"
assert checkio('www', 3) == 0.56, "3rd example"
assert checkio('bbbb', 1) == 0, "4th example"
assert checkio('wwbb', 4) == 0.5, "5th example"
assert checkio('bwbwbwb', 5) == 0.48, "6th example"
April 13, 2016
