1009. Complement of Base 10 Integer #

Problem #

The complement of an integer is the integer you get when you flip all the 0's to 1's and all the 1's to 0's in its binary representation.

• For example, The integer 5 is "101" in binary and its complement is "010" which is the integer 2.

Given an integer n, return its complement.

Example 1:

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

Example 2:

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

Example 3:

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

Constraints:

• 0 <= n < 109

Problem Summary #

Every non-negative integer N has its binary representation. For example, 5 can be represented in binary as “101”, 11 can be represented in binary as “1011”, and so on. Note that, except for N = 0, no binary representation contains leading zeros.

The binary complement is obtained by changing every 1 to 0 and every 0 to 1. For example, the binary complement of the binary number “101” is “010”.

Given a decimal number N, return the decimal integer corresponding to the complement of its binary representation.

Solution Approach #

• Easy problem. To find the complement of a decimal number, we only need to XOR the number with a number consisting entirely of 1s. Therefore, the key point of this problem is how to construct the mask.

Code #

package leetcode

func bitwiseComplement(n int) int {
    mask := 1 
    for mask < n {
        mask = (mask << 1) + 1
    }
    return mask ^ n
}