## 1009. 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:5Output:2Explanation:5 is "101" in binary, with complement "010" in binary, which is 2 in base-10.

**Example 2:**

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

**Example 3:**

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

**Note:**

`0 <= N < 10^9`

- This question is the same as 476: https://leetcode.com/problems/number-complement/

## Rust Solution

```
struct Solution;
impl Solution {
fn bitwise_complement(n: i32) -> i32 {
if n == 0 {
return 1;
}
let mut mask = !0;
while mask & n != 0 {
mask <<= 1;
}
mask = !mask;
mask ^ n
}
}
#[test]
fn test() {
assert_eq!(Solution::bitwise_complement(5), 2);
assert_eq!(Solution::bitwise_complement(7), 0);
assert_eq!(Solution::bitwise_complement(10), 5);
assert_eq!(Solution::bitwise_complement(0), 1);
}
```

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