Why is the counter not increasing in this binary search code in python?

Question

def binary_search(array,key,left,right):
    if left>right:
        return -1
    mid=(right+left)//2

    if key==array[mid]:
        return mid
    i=0
    if key<array[mid]:
        i+=1
        print("subarray at step {} : {}".format(i,array[left:mid]))
        return binary_search(array,key,left,mid-1)

    elif key>array[mid]:
        i+=1
        print("subarray at step {} : {}".format(i,array[mid:right]))
        return binary_search(array,key,mid+1,right)



array=[1,2,3,4,5,6,7,8,9,11,22,33,44,55,66,77,88,99,222,333]
res= binary_search(array,88,0,len(array))

print(res if res!=-1 else "Not found")

In this binary search code, I couldn't figure out why the counter wan not working. Each time the i is printed a 1. The counter doesn't increase. What am I doing wrong? Thank you.

Answer 1

i is being printed as 1 because you are i is being set to 0 inside binary_search function on each call. try moving out initiaization of i outside the function.

def binary_search(array,key,left,right):
    global i
    if left>right:
        return -1
    mid=(right+left)//2

    if key==array[mid]:
        return mid
    # i=0
    if key<array[mid]:
        i+=1
        print("subarray at step {} : {}".format(i,array[left:mid]))
        return binary_search(array,key,left,mid-1)

    elif key>array[mid]:
        i+=1
        print("subarray at step {} : {}".format(i,array[mid:right]))
        return binary_search(array,key,mid+1,right)


i =0
array=[1,2,3,4,5,6,7,8,9,11,22,33,44,55,66,77,88,99,222,333]
res= binary_search(array,88,0,len(array))

You need to change the scope of variable i to make it global.

Answer 2

make i as global variable and to assing valuable call global keywoard

i = 0
def binary_search(array,key,left,right):
    if left>right:
        return -1
    mid=(right+left)//2
    # i=0

    if key==array[mid]:
        return f'it found position {mid}'
    
    if key<array[mid]:
        global i 
        i = i+1
        print("subarray at step {} : {}".format(i,array[left:mid]))
        return binary_search(array,key,left,mid-1)

    elif key>array[mid]:
        i+=1
        print("subarray at step {} : {}".format(i,array[mid:right]))
        return binary_search(array,key,mid+1,right)



array=[1,2,3,4,5,6,7,8,9,11,22,33,44,55,66,77,88,99,222,333]
res= binary_search(array,88,0,len(array))
print(len(array))

print(res if res!=-1 else "Not found")