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def solution(str_n):
# 3 possibles operations:
# - Add one fuel
# - Remove one fuel
# - Divide fuel by 2 (allowed only if fuel is an even number)
fuel = int(str_n)
actions = 0
# Execute until we get 1 fuel remaining
while fuel != 1:
# If fuel is not an even number, we need to add or remove one fuel
if fuel % 2 != 0:
# We have to check if it is more interesting to add or remove one fuel, depending on the result of (fuel + 1) % 2 and (fuel - 1)
# i.e. 13 -> Adding 1 = 14 ; 14 // 2 = 7 ; we'd need to update 7 to get an even number
# 13 -> Removing 1 = 12 ; 12 // 2 = 6 ; we wouldn't need to add change 6
# If removing one is more efficient
if ((fuel - 1) // 2) % 2 == 0:
fuel -= 1
actions += 1
# Exception! If it results in 2, then it is more efficient to go from 3 to 2
elif fuel - 1 == 2:
fuel -= 1
actions += 1
# if not, we add one
else:
fuel += 1
actions += 1
# Consume fuel
fuel //= 2
actions += 1
return actions
print(solution('4'), "should equal 2")
print(solution('15'), "should equal 5")
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