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
  2. 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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