weightSorter.py

# See https://twitter.com/octonion/status/555961809141002240 and https://twitter.com/octonion/status/555990175147642880

lightWeight = 10.0
heavyWeight = lightWeight + 1.0


def sortPairs(pair1, pair2, pair3):
    heavies = []
    balance1 = balance([pair1[0], pair2[0]], [pair1[1], pair3[0]])
    if balance1 == 'balanced':
        balance2 = balance([pair1[0]], [pair1[1]])
        if balance2 == 'left':
            heavies = [pair1[0], pair2[1], pair3[0]]
        else:
            heavies = [pair1[1], pair2[0], pair3[1]]
    else:
        balance2 = balance([pair2[0], pair3[0]], [pair1[0], pair1[1]])
        if balance2 == 'balanced':
            if balance1 == 'left':
                heavies = [pair1[0], pair2[0], pair3[1]]
            else:
                heavies = [pair1[1], pair2[1], pair3[0]]
        elif balance2 == 'left':
            if balance1 == 'left':
                heavies = [pair1[0], pair2[0], pair3[0]]
            else:
                heavies = [pair1[1], pair2[0], pair3[0]]
        else:
            if balance1 == 'left':
                heavies = [pair1[0], pair2[1], pair3[1]]
            else:
                heavies = [pair1[1], pair2[1], pair3[1]]
    return heavies
    

def balance(leftSide, rightSide):
    leftWeight = sum(leftSide)
    rightWeight = sum(rightSide)
    print "left: " + str(leftWeight) + ", right: " + str(rightWeight)
    if (leftWeight > rightWeight):
        return 'left'
    if (leftWeight < rightWeight):
        return 'right'
    return 'balanced'


for pair1 in [[lightWeight, heavyWeight], [heavyWeight, lightWeight]]:
    for pair2 in [[lightWeight, heavyWeight], [heavyWeight, lightWeight]]:
        for pair3 in [[lightWeight, heavyWeight], [heavyWeight, lightWeight]]:
            print 'testing pair 1 ' + str(pair1) + ', pair2 ' + str(pair2) + ', pair3 ' + str(pair3)
            heavies = sortPairs(pair1, pair2, pair3)
            for heavy in heavies:
                assert heavy == heavyWeight, 'You are wrong about a heavy. heavies: ' + str(heavies) + ', light: ' + str(lights)

print 'Success!'


#def sortPairsBad(pair1, pair2, pair3):
#  leftSide = [pair1[0], pair2[0], pair3[0]]
#  rightSide = [pair1[1], pair2[1], pair3[1]]
#
#  balance1 = balance(leftSide, rightSide)
#  assert balance1 != 'balanced', 'Scale says ' + balance1 + ', my assumption must be wrong! left: ' + str(leftSide) + ', right: ' + str(rightSide)
#  heavies = leftSide[:] # copy array with slice
#  lights = rightSide[:]
#  if (balance1 == 'right'):
#    heavies = rightSide[:]
#    lights = leftSide[:]
#
#  # swap one value
#  swapTemp = lights[0]
#  lights[0] = heavies[0]
#  heavies[0] = swapTemp
#
#  balance2 = balance(heavies, lights)
#  assert balance2 != 'balanced', 'Scale says ' + balance2 + ', my assumption must be wrong!  left: ' + str(heavies) + ', right: ' + str(lights)
#  if (balance2 == 'right'):
#    # balance changed, meaning we swapped the wrong one
#    heavies[0] = lights[0]
#    lights[0] = swapTemp
#  return (heavies, lights)