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54 lines
1.4 KiB
Python
54 lines
1.4 KiB
Python
"""
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Project Euler Problem 4: https://projecteuler.net/problem=4
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Largest palindrome product
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A palindromic number reads the same both ways. The largest palindrome made
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from the product of two 2-digit numbers is 9009 = 91 × 99.
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Find the largest palindrome made from the product of two 3-digit numbers.
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References:
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- https://en.wikipedia.org/wiki/Palindromic_number
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"""
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def solution(n: int = 998001) -> int:
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"""
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Returns the largest palindrome made from the product of two 3-digit
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numbers which is less than n.
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>>> solution(20000)
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19591
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>>> solution(30000)
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29992
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>>> solution(40000)
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39893
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>>> solution(10000)
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Traceback (most recent call last):
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...
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ValueError: That number is larger than our acceptable range.
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"""
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# fetches the next number
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for number in range(n - 1, 9999, -1):
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str_number = str(number)
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# checks whether 'str_number' is a palindrome.
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if str_number == str_number[::-1]:
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divisor = 999
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# if 'number' is a product of two 3-digit numbers
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# then number is the answer otherwise fetch next number.
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while divisor != 99:
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if (number % divisor == 0) and (len(str(number // divisor)) == 3.0):
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return number
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divisor -= 1
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raise ValueError("That number is larger than our acceptable range.")
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if __name__ == "__main__":
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print(f"{solution() = }")
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