CODEWITHSUNDEEP
python
DikiyStoyak
DikiyStoyak

Reputation: 113

I found a mistake in the book "Grokking Algorithms"

I am beginner in programming. I am reading the book "Grokking algorithms" by Aditya Y Bhargava." And in the first code I found a mistake. The book describes binary algorithm. It says that the algorithm must takes the average of an array and then average of that average, but I debbuged the code and it just takes a very big number of array and then reduces it by 1. Maybe it is a difference between versions, because I use Python 3.7, but in the book it is Python 2.7

def binary_search(list, item):
    low = 0
    high = len(list)-1

    while low <= high:
        mid = int(low + high)
        guess = list[mid]
        if guess == item:
            return mid
        if guess > item:
            high = mid - 1
        else:
            low = mid + 1

    return None

my_list = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

print(binary_search(my_list, 1))

Upvotes: 11

Views: 2961

Answers (2)

Ismoil Shokirov
Ismoil Shokirov

Reputation: 3031

Yes, I have just started reading this book and stumbled upon this issue. Basically, there are 2 errors:

In the book where it first shows an example of getting average it is:

mid = (low + high) / 2   #Should be mid = (low + high) // 2

/ - Division (float): divides the first operand by the second

// - Division (floor): divides the first operand by the second

And second error as it was already answered:

mid = (low + high)   #Should be mid = (low + high) // 2

More errors at https://adit.io/errata.html

Upvotes: 3

Matt Hall
Matt Hall

Reputation: 8152

The errata for the book lists this as an error. It should be:

mid = (low + high) // 2

So: good catch!

And, spoiler alert: there are more errors!

Upvotes: 15

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