49 lines
1.1 KiB
Python
49 lines
1.1 KiB
Python
"""
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Even Fibonacci Numbers
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Each new term in the Fibonacci sequence is generated by adding the previous two terms. By starting with 1 and 2, the first 10 terms will be:
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1, 2, 3, 5, 8, 13, 21, 34, 55, 89
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By considering the terms in the Fibonacci sequence whose values do not exceed four million, find the sum of the even-valued terms.
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"""
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UP_NUM = 4000000
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def is_even(num: int) -> bool:
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"""Check if a number is even."""
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return num & 1 == 0
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"""
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下面这个方法实在太慢，计算400万项还会内存溢出。
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```python
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def fibonacci_sequence(n: int) -> list[int]:
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a, b = 1, 2
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res = [a, b]
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while b <= n:
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a, b = b, a + b
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res.append(b)
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return res
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def main():
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fib_seq = fibonacci_sequence(UP_NUM)
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even_sum = sum(num for num in fib_seq if is_even(num))
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print(even_sum)
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```
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"""
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def even_fibonacci(limit: int) -> int:
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a, b = 1, 2
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even_sum = 0
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while b <= limit:
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if is_even(b):
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even_sum += b
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a, b = b, a + b
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return even_sum
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if __name__ == "__main__":
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print(even_fibonacci(UP_NUM))
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