# LeetCode 1009. Complement of Base 10 Integer

## Description

https://leetcode.com/problems/complement-of-base-10-integer/

Every non-negative integer `N` has a binary representation.  For example, `5` can be represented as `"101"` in binary, `11` as `"1011"` in binary, and so on.  Note that except for `N = 0`, there are no leading zeroes in any binary representation.

The complement of a binary representation is the number in binary you get when changing every `1` to a `0` and `0` to a `1`.  For example, the complement of `"101"` in binary is `"010"` in binary.

For a given number `N` in base-10, return the complement of it’s binary representation as a base-10 integer.

Example 1:

```Input: 5
Output: 2
Explanation: 5 is "101" in binary, with complement "010" in binary, which is 2 in base-10.
```

Example 2:

```Input: 7
Output: 0
Explanation: 7 is "111" in binary, with complement "000" in binary, which is 0 in base-10.
```

Example 3:

```Input: 10
Output: 5
Explanation: 10 is "1010" in binary, with complement "0101" in binary, which is 5 in base-10.
```

Note:

1. `0 <= N < 10^9`
2. This question is the same as 476: https://leetcode.com/problems/number-complement/

## Explanation

Find complement’s binary string and then convert it back to integer.

## Python Solution

``````class Solution:
def bitwiseComplement(self, N: int) -> int:

binary_n = bin(N)

result = ""
for c in binary_n[2:]:
if c == '0':
result += '1'
else:
result += '0'

return int(result, 2)``````
• Time Complexity: O(N).
• Space Complexity: O(N).