二分搜索是一种用于在排序列表中搜索元素的技术。在本文中，我们将着眼于进行二分搜索的库函数。
查找元素的第一次出现。
bisect.bisect_left(a, x, lo=0, hi=len(a)) : Returns leftmost insertion point of x in a sorted list. Last two parameters are optional, they are used to search in sublist.
# Python code to demonstrate working
# of binary search in library
from bisect import bisect_left
def BinarySearch(a, x):
i = bisect_left(a, x)
if i != len(a) and a[i] == x:
return i
else:
return -1
a = [1, 2, 4, 4, 8]
x = int(4)
res = BinarySearch(a, x)
if res == -1:
print(x, "is absent")
else:
print("First occurrence of", x, "is present at", res)
输出：
First occurrence of 4 is present at 2
寻找小于 x 的最大值。
# Python code to demonstrate working
# of binary search in library
from bisect import bisect_left
def BinarySearch(a, x):
i = bisect_left(a, x)
if i:
return (i-1)
else:
return -1
# Driver code
a = [1, 2, 4, 4, 8]
x = int(7)
res = BinarySearch(a, x)
if res == -1:
print("No value smaller than ", x)
else:
print("Largest value smaller than ", x, " is at index ", res)
输出：
Largest value smaller than 7 is at index 3
寻找最右边的出现
bisect.bisect_right(a, x, lo=0, hi=len(a)) Returns rightmost insertion point of x in a sorted list a. Last two parameters are optional, they are used to search in sublist.
# Python code to demonstrate working
# of binary search in library
from bisect import bisect_right
def BinarySearch(a, x):
i = bisect_right(a, x)
if i != len(a)+1 and a[i-1] == x:
return (i-1)
else:
return -1
a = [1, 2, 4, 4]
x = int(4)
res = BinarySearch(a, x)
if res == -1:
print(x, "is absent")
else:
print("Last occurrence of", x, "is present at", res)
输出：
Last occurrence of 4 is present at 3
请参考 Binary Search 来编写您自己的 Binary Search 代码。
参考 ：
https://文档。Python.org/3/library/bisect.html
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