CheckIO - O'Reilly Challenge 2 : Ghost Age

checkio.2.02.ghostAge.py

# CheckIO - O'Reilly Challenge 2 : Ghost Age
# http://checkio.org

# Nicola takes a moment to study the ghosts. 
# He is trying to think up a new method to determine just how old these ghosts are. 
# He knows that their age is somehow related to their opacity. 
# To measure their opacity Nikola uses a scale of 10000 units to 0 units, 
# where 10000 is a completely opaque newborn ghost (0 years old) and 0 is completely transparent.
# After some experimenting, Nikola thinks he has discovered the law of ghostly opacity. 
# On every birthday, a ghost's opacity is reduced by a number of units 
# equal to its age when its age is a Fibonacci number or increased by 1 if it is not.
# Precondition:age < 5000
# 0 < opacity ≤ 10000

# Get Fibonacci number n
def nextFibo(n):
    if n<2: return n
    else:   return nextFibo(n-1) + nextFibo(n-2)

def checkio(limit):
    age=0
    lastFibo=1
    indexFibo=2
    opacity=10000
    while opacity!=limit: # While I dont found transparency number...
        age+=1
        if age==lastFibo: # -age if age is a Fibonacci number
            opacity-=age
            indexFibo+=1
            lastFibo=nextFibo(indexFibo)    
        else: # +1 in other case
            if opacity<10000: # Keeping opacity value into the limis
                opacity+=1
    return age

#These "asserts" using only for self-checking and not necessary for auto-testing
if __name__ == '__main__':
    assert checkio(9995) == 4, "4 years"
    assert checkio(3703) == 4665, "4665 years"