created and first commit(3 solusions)

solutions/0002.even_fibonacci/euler_2.py

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