README.md

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: 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

Solutions (Rust)

1. Mathematical

impl Solution {
    pub fn bitwise_complement(n: i32) -> i32 {
        match n {
            0 => 1,
            _ => 2_i32.pow((n as f64).log2() as u32 + 1) - 1 - n,
        }
    }
}

2. Bitwise Operator

impl Solution {
    pub fn bitwise_complement(n: i32) -> i32 {
        let mut ret = 0;

        for i in 0..31 {
            if n >> i == 0 && i > 0 {
                break;
            }
            if n & (1 << i) == 0 {
                ret ^= 1 << i;
            }
        }

        ret
    }
}