Binary Search (bisect) in Python
Last Updated :
04 Feb, 2022
Binary Search is a technique used to search element in a sorted list. In this article, we will looking at library functions to do Binary Search.
Finding first occurrence of an element.
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.
Python3
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)
|
Output:
First occurrence of 4 is present at 2
Finding greatest value smaller than x.
Python3
from bisect import bisect_left
def BinarySearch(a, x):
i = bisect_left(a, x)
if i:
return (i-1)
else:
return -1
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)
|
Output:
Largest value smaller than 7 is at index 3
Finding rightmost occurrence
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.
Python3
from bisect import bisect_right
def BinarySearch(a, x):
i = bisect_right(a, x)
if i != 0 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)
|
Output:
Last occurrence of 4 is present at 3
Please refer Binary Search for writing your own Binary Search code.
Reference :
https://docs.python.org/3/library/bisect.html
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