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.
# 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) |
First occurrence of 4 is present at 2
Finding greatest value smaller than x.
# 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) |
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.
# 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) |
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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