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55 lines
1.3 KiB
Python
55 lines
1.3 KiB
Python
"""
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Ugly numbers are numbers whose only prime factors are 2, 3 or 5. The sequence
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1, 2, 3, 4, 5, 6, 8, 9, 10, 12, 15, … shows the first 11 ugly numbers. By convention,
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1 is included.
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Given an integer n, we have to find the nth ugly number.
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For more details, refer this article
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https://www.geeksforgeeks.org/ugly-numbers/
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"""
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def ugly_numbers(n: int) -> int:
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"""
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Returns the nth ugly number.
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>>> ugly_numbers(100)
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1536
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>>> ugly_numbers(0)
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1
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>>> ugly_numbers(20)
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36
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>>> ugly_numbers(-5)
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1
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>>> ugly_numbers(-5.5)
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Traceback (most recent call last):
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...
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TypeError: 'float' object cannot be interpreted as an integer
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"""
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ugly_nums = [1]
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i2, i3, i5 = 0, 0, 0
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next_2 = ugly_nums[i2] * 2
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next_3 = ugly_nums[i3] * 3
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next_5 = ugly_nums[i5] * 5
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for _ in range(1, n):
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next_num = min(next_2, next_3, next_5)
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ugly_nums.append(next_num)
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if next_num == next_2:
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i2 += 1
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next_2 = ugly_nums[i2] * 2
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if next_num == next_3:
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i3 += 1
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next_3 = ugly_nums[i3] * 3
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if next_num == next_5:
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i5 += 1
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next_5 = ugly_nums[i5] * 5
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return ugly_nums[-1]
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if __name__ == "__main__":
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from doctest import testmod
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testmod(verbose=True)
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print(f"{ugly_numbers(200) = }")
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