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39 lines
836 B
Python
39 lines
836 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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