我正在尝试执行二进制搜索以在循环排序的数组中查找元素。我得到一个我似乎不理解的类型错误。任何建议/修改将不胜感激。
这是我的代码:
def Binarysearch(a, low, high, x):
if low > high:
return -1
else:
mid = (low + high)/2
if x == a[mid]:
return mid
elif a[mid] <= a[high]:
if x > a[mid] and x <= a[high]:
return Binarysearch(a, mid+1, high, x)
elif a[mid] >= a[low]:
if x >= a[low] and x < a[mid]:
return Binarysearch(a, low, mid-1, x)
elem_list = [6, 11, 12, 13, 14, 15, 16, 1, 2, 3, 4, 5]
x = int(raw_input('enter search elemet'))
lenlist = len(elem_list)
result = Binarysearch(elem_list, 0, lenlist-1, x)
if result == -1:
print "Not found"
else:
print "Found it", elem_list[result]
我收到错误:
Line32: TypeError: list indices must be integers, not NoneType
答案 0 :(得分:1)
除非这是学习练习,否则您可能希望使用bisect
模块。 e.g。
from bisect import bisect_left
def search(l, x): # search x in l
if len(l) > 0:
p = min((e,i) for i,e in enumerate(l))[1] # min element index
p1 = bisect_left(l, x, 0, p) # search left
if p1 < p and l[p1]==x:
return p1
p2 = bisect_left(l, x, p) # search right
if p2 < len(l) and l[p2]==x:
return p2
互动演示:
>>> elem_list = [6, 11, 12, 13, 14, 15, 16, 1, 2, 3, 4, 5]
>>> for e in elem_list:
... assert e == elem_list[search(elem_list, e)]
...
>>> for e in [-1, 7, 8, 999]:
... assert None == search(elem_list, e)
...
>>> elem_list.sort()
>>> elem_list
[1, 2, 3, 4, 5, 6, 11, 12, 13, 14, 15, 16]
>>> for e in elem_list:
... assert e == elem_list[search(elem_list, e)]
...
>>> for e in [-1, 7, 8, 999]:
... assert None == search(elem_list, e)
...
>>> assert None == search([], 123)
另见
答案 1 :(得分:0)
def rotated_binary_search(A, N, key):
L = 0
R = N - 1
while (L <= R):
M = L + ((R - L) / 2)
if (A[M] == key): return M
# the bottom half is sorted
if (A[L] <= A[M]):
if (A[L] <= key and key < A[M]):
R = M - 1
else:
L = M + 1
# the upper half is sorted
else:
if (A[M] < key and key <= A[R]):
L = M + 1
else:
R = M - 1
return -1
A = [6, 11, 12, 13, 14, 15, 16, 1, 2, 3, 4, 5]
N = len(A)
result = rotated_binary_search(A, N, 13)
print "Original List", A
if result == -1:
print "Not found"
else:
print "Found", A[result], "at position", result`enter code here`
结果:
Original List [6, 11, 12, 13, 14, 15, 16, 1, 2, 3, 4, 5]
Found 13 at position 3