binary_search_by_index.py

# from https://web.facebook.com/groups/ThaiPGAssociateSociety/permalink/1683383838539545/
def binarySearch (A, l, r): 
    if r >= l: 
  
        k = l + (r - l) // 2
    
        if k + 1 == A[k]:
            return k 
          
        elif k + 1 > A[k] : 
            return binarySearch(A, k + 1, r) 
        else: 
            return binarySearch(A, l, k-1) 
    else: 
        return -1
      
arr = [-4,-3,-1,0,1,2,6,8,11,13,14,19,20,24,26,35,48,49,80,90,92]
assert binarySearch(arr, 0, len(arr) - 1) == 7

arr = [0]
assert binarySearch(arr, 0, len(arr) - 1)  == -1

arr = [1]
assert binarySearch(arr, 0, len(arr) - 1)  == 0 

index start with 1