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fibonacci_sequence.py
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fibonacci_sequence.py
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def fibonacci(n):
# 时间复杂度为O(2^N)
if n < 0:
return "Incorrect input"
elif n == 1:
return 0
elif n == 2:
return 1
else:
return fibonacci(n-1)+fibonacci(n-2)
def fibonacci_a(n):
# 空间复杂度为O(N), 使用数组存每一个值, 时间复杂度为O(N)
if n <= 0:
return 'Incorrect input'
elif n == 1:
return 0
elif n == 2:
return 1
else:
nums = [0] * (n+1)
nums[0], nums[1] = 0, 1
i = 2
while i <= n:
nums[i] = nums[i-1] + nums[i-2]
i += 1
return nums[n-1]
def fibonacci_b(n):
# 空间复杂度为O(1), 时间复杂度为O(N)
if n <= 0:
return 'Incorrect input'
elif n == 1:
return 0
elif n == 2:
return 1
else:
a, b = 0, 1
while True:
temp = b
b = a + b
a = temp
n -= 1
if n <= 2:
break
return b
print(fibonacci(5))
print(fibonacci_a(5))
print(fibonacci_b(5))