Pythonは二分検索(再帰と非再帰)を実現
二分検索は毎回半分のデータを排除でき,検索の効率は非常に高いが,限界は大きい.二分検索を使用するには、順序付きシーケンスでなければなりません.
1.
def binary_search(lis, nun):
left = 0
right = len(lis) - 1
while left <= right: #
mid = (left + right) // 2 # , ( )
if num < lis[mid]: # , ,
right = mid - 1 # , mid-1
elif num > lis[mid]: # ,
left = mid + 1 # , mid+1
else:
return mid # ,
return -1 # , ,
lis = [11, 32, 51, 21, 42, 9, 5, 6, 7, 8]
print(lis)
lis.sort()
print(lis)
while 1:
num = int(input(' :'))
res = binary_search(lis, num)
print(res)
if res == -1:
print(' !')
else:
print(' !')
2.
def binary_search(lis, left, right, num):
if left > right: #
return -1
mid = (left + right) // 2
if num < lis[mid]:
right = mid -1
elif num > lis[mid]:
left = mid + 1
else:
return mid
return binary_search(lis, left, right, num)
# return , None
# , return, None
lis = [11, 32, 51, 21, 42, 9, 5, 6, 7, 8]
print(lis)
lis.sort()
print(lis)
while 1:
num = int(input(' :'))
res = binary_search(lis, 0, len(lis)-1,num)
print(res)
if res == -1:
print(' !')
else:
print(' !')