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35 lines
813 B
Python
35 lines
813 B
Python
#Factorial of a number using memoization
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result=[-1]*10
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result[0]=result[1]=1
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def factorial(num):
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"""
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>>> factorial(7)
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5040
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>>> factorial(-1)
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'Number should not be negative.'
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>>> [factorial(i) for i in range(5)]
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[1, 1, 2, 6, 24]
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"""
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if num<0:
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return "Number should not be negative."
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if result[num]!=-1:
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return result[num]
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else:
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result[num]=num*factorial(num-1)
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#uncomment the following to see how recalculations are avoided
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#print(result)
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return result[num]
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#factorial of num
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#uncomment the following to see how recalculations are avoided
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##result=[-1]*10
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##result[0]=result[1]=1
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##print(factorial(5))
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# print(factorial(3))
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# print(factorial(7))
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if __name__ == "__main__":
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import doctest
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doctest.testmod()
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