binarysearch.py

#!/usr/bin/env python3
# -*- coding: utf-8 -*-
"""
Created on Mon Feb 24 13:32:09 2020

@author: rasmuskaarelkilp
"""

#We basically ignore half of the elements just after one comparison.

#Compare x with the middle element.
#If x matches with middle element, we return the mid index.
#Else If x is greater than the mid element, then x can only lie in right half subarray after the mid element. So we recur for right half.
#Else (x is smaller) recur for the left half.
# Python Program for recursive binary search. 
  
# Returns index of x in arr if present, else -1 
def binarySearch (arr, l, r, x): 
  
    # Check base case 
    if r >= l: 
  
        mid = l + (r - l)/2
  
        # If element is present at the middle itself 
        if mid == x: 
            return mid 
          
        # If element is smaller than mid, then it can only 
        # be present in left subarray 
        elif mid > x: 
            return binarySearch(arr, l, mid-1, x) 
  
        # Else the element can only be present in right subarray 
        else: 
            return binarySearch(arr, mid+1, r, x) 
  
    else: 
        # Element is not present in the array 
        return -1
  
# Test array 
arr = [ 2, 3, 4, 10, 40 ] 
x = 10
  
# Function call 
result = binarySearch(arr, 0, len(arr)-1, x) 
  
if result != -1: 
    print ("Element is present at index %d" % result )
else: 
    print ("Element is not present in array")