Binary search
We repeatedly determining which half of the list the item is in.
""" Binary search / Algorithm
Binary search works only for ordered lists key search.
A linear search of a shelf with 100 books takes 100 steps.
A binary search on 50 takes 6 and on 100 only 7 steps.
"""
import time
def timer(func):
def wrapper(*args, **kwargs):
t1 = time.time()
res = func(*args, **kwargs)
print(func.__name__ + "():\t", time.time() - t1, "s")
return res
return wrapper
@timer
def binary_search(needle, haystack):
i = 0
j = len(haystack) - 1
while True:
m = (i + j) // 2
if needle > haystack[m]: i = m + 1
if needle < haystack[m]: j = m - 1
if needle == haystack[m]:
return m
if i > j:
return None
@timer
def linear_search(needle, haystack):
for i in range(len(haystack)):
if needle == haystack[i]:
return i
return None
@timer
def generate_data():
data = [i for i in range(123456789)]
return data
# Tests
data = [1, 4, 8, 11, 13, 16, 19, 19]
assert binary_search(1, data) == 0
assert binary_search(19, data) == 6
assert binary_search(100, data) == None
print("Tests passed")
# Time
lst = generate_data()
k1= binary_search(123456780, lst)
k2 = linear_search(123456780, lst)
assert k1 == k2
"""
generate_data() time: 5.986196041107178 s
binary_search() time: 1.8835067749023438e-05 s
linear_search() time: 8.184731483459473 s
"""
Last update: 423 days ago