What's wrong with my python code (Add binary)?

Question

It's a very simple problem from leetcode:

Given two binary strings, return their sum (also a binary string).

For example, a = "11" b = "1" Return "100".

Here is my code, I think it's just okay

def addBinary(self, a, b):
    if len(a) < len(b):
        a, b = b, a
            
    rev, temp, sum = list(a[::-1]), 0, ""
        
    for i, j in enumerate(b[::-1]):
        temp = temp + int(rev[i]) + int(j)
        if temp == 0 or 1:
            rev[i] = str(temp)
            temp = 0
            x2 = temp
        elif temp == 2:
            rev[i] = "0"
            temp = 1
            
    if temp == 1:
        rev = rev + ["1"]
        
    for digit in rev[::-1]:
        sum += digit
        
    return sum

However as I run, a test can't pass

Input: "1", "1"

Output: "2"

Expected: "10"

I simply don't know why and set a break point, finding that though "temp = temp + int(rev[i]) + int(j)", temp was equalled to 2, it didn't go to the elif part of the condition and thus returns "2" as the final result.

Could anyone tell me why? I really appreciate that.

`if temp == 0 or 1:` doesn't do what you think it does. See the dupe for details. — user2357112, May 20 '15 at 21:11

score 2 · Accepted Answer · answered May 20 '15 at 21:11

2

You have a typo

if temp == 0 or 1:

should instead be:

if temp == 0 or temp == 1:

answered May 20 '15 at 21:11

Aaron D

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thanks a lot, maybe I should ( ) them as well – tonyabracadabra May 20 '15 at 21:20
`if temp in (0,1)` is nice, too. – TigerhawkT3 May 20 '15 at 21:30

score 0 · Answer 2 · answered May 20 '15 at 21:12

0

A simple and more pythonic way of doing the same is:

def add_binary(a, b):
    return bin(int(a) + int(b))[2:]

print add_binary("1", "1")
>>> 10

answered May 20 '15 at 21:12

ZdaR

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@PaulSasik: No, it's supposed to be "10". "100" is the expected output for inputs "11" and "1". – user2357112 May 20 '15 at 21:14
@PaulSasik you are doubting on Python binary arithmetic ? – ZdaR May 20 '15 at 21:15
@anmol_uppal: No, I'm doubting why you chose a different set of input than the OP? – Paul Sasik May 20 '15 at 21:16
@PaulSasik: Look further down in the question. "1" and "1" is the specific failing test case. – user2357112 May 20 '15 at 21:17
@PaulSasik Because the OP had given 2 sample inputs and I just tried out the latter one, read the bottom line of the question. – ZdaR May 20 '15 at 21:18
Long day. Sorry guys. What's the down vote about? I didn't run it but your code seem legit. – Paul Sasik May 20 '15 at 21:19
Don't worry it happens, and comments from downvoters ? – ZdaR May 20 '15 at 21:19

What's wrong with my python code (Add binary)?

2 Answers2