Get a Fibonacci number with O(n).

fibonacci_with_linear_order.py

# coding: utf-8

"""Gets Fibonacci numbers with a linear Order.
"""


def get_fibonacci(n): 
    a = 0
    b = 1
    for i in range(0, n): 
        a, b = b, a + b

    return a


if __name__ == '__main__': 
    import unittest

    class FibonacciTestCase(unittest.TestCase): 

        def test_get_fibonacci(self): 
            pairs = [
              [0, 0],
              [1, 1],
              [2, 1],
              [3, 2],
              [4, 3],
              [5, 5],
              [6, 8],
              [7, 13],
              [8, 21],
            ]

            for n, expected in pairs: 
                self.assertEqual(get_fibonacci(n), expected)

    unittest.main()