what is wrong with my binary search python code

Question

I am constantly getting the wrong output in my binary search program. The output is always None even when the key element is present. Have a look at my code and help, please.

guess=1
def binary_search(n,key):
    low=0
    high=len(n)-1
    
    while(low <= high):
        mid=(low+high)//2
        guess=n[mid]
        if(guess==key):
            return mid
        elif (guess<key):
            high=mid-1
        elif(guess>key):
            low=mid+1
    return None

n=[1,3,5,7,9]
print(binary_search(n,3))

I literally opened an answer to type exactly the same thing... — 2e0byo
– 2e0byo, Commented Sep 23, 2021 at 15:55

Albin Paul · Accepted Answer · 2021-09-23 15:50:00Z

4

Your search conditions are wrong. if guess>key then you need to decrease the guess my setting high=mid-1 and increase the guess with low=mid+1 if guess<key.

guess=1
def binary_search(n,key):
    low=0
    high=len(n)-1
    
    while(low <= high):
        mid=(low+high)//2
        guess=n[mid]
        if(guess==key):
            return mid
        elif (guess>key):
            high=mid-1
        elif(guess<key):
            low=mid+1
    return None

n=[1,3,5,7,9]
print(binary_search(n,3))

answered Sep 23, 2021 at 15:50

Albin Paul

3,4292 gold badges17 silver badges34 bronze badges

Sign up to request clarification or add additional context in comments.

4 Comments

MisterMiyagi Over a year ago

In other words, they need to swap + and - or < and >?

Albin Paul Over a year ago

@MisterMiyagi that wouldnt work. setting high=mid+1 doesnt make sense. if key < mid then high = mid - 1 else low = mid+1.

MisterMiyagi Over a year ago

So the second case, they need to swap the < and >?

Albin Paul Over a year ago

@MisterMiyagi Yes

Collectives™ on Stack Overflow

what is wrong with my binary search python code

1 Answer 1

4 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

4 Comments

Your Answer

Sign up or log in

Post as a guest

Related