我在Python中進行思考練習,用Memo來計算Fibonacci序列比不使用一個更有效。但是當實施它並測試所消耗的時間時,我發現運行時間根本沒有減少。我知道我的程序肯定有問題,有人可以告訴我我哪裏出了錯。非常感謝。爲什麼我的備忘錄根本沒有提高效率?
import time
known = {0:0,1:1}
def fibonacci_memo(n):
"""return the nth number of fibonacci sequence
using memo to raise efficiency"""
if n in known:
return known[n]
res = fibonacci(n-1) + fibonacci(n-2)
known[n] = res
return res
def fibonacci(n):
"""return the nth number of fibonacci sequence
without using memo"""
if n == 0:
return 0
if n == 1:
return 1
return fibonacci(n-1) + fibonacci(n-2)
if __name__ == '__main__':
start = time.clock()
print fibonacci_memo(32)
elaspsed = time.clock() - start
print 'using memo time used: ' + str(elaspsed)
start = time.clock()
print fibonacci(32)
elaspsed = time.clock() - start
print 'without using memo time used: ' + str(elaspsed)
輸出是一樣的東西:
2178309
using memo time used: 1.83040345779
2178309
without using memo time used: 1.792043347