Formatted question description: https://leetcode.ca/all/1009.html

# 1009. Complement of Base 10 Integer

## Level

Easy

## Description

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 its 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:**

`0 <= N < 10^9`

## Solution

Since the complement of `0`

is `1`

and the complement of `1`

is `0`

, simply deal with these two numbers first.

For the other non-negative integers, consider the number of bits in binary representation, which can be calculated by using log_{2}*N* + 1 for integer `N`

(keep the integer part of the calculated result). For a number with `b`

bits in binary representation, the sum of the number and its complement equals 2^{b} - 1, so the complement equals 2^{b} - 1 minus the given number.

```
class Solution {
public int bitwiseComplement(int N) {
if (N <= 1)
return 1 - N;
int power = (int) (Math.log(N) / Math.log(2));
int max = (int) (Math.pow(2, power + 1) - 1);
return max - N;
}
}
```