Marc Lester Tan

Here’s another easy problem which can be solved by applying logical operators.

class Solution {
    fun findComplement(num: Int): Int {
        return if(num == Integer.MAX_VALUE) 
            num xor Integer.MAX_VALUE 
        else {
            var allOnes = 0
            for(number in 0..31){
                val p = Math.pow(2.0, number.toDouble()) - 1
                if(p >= num) {
                    allOnes = p.toInt()
                    break
                }    
            }
            
            num xor allOnes.toInt()
        }
    }
}

Runtime: 124 ms, faster than 100.00% of Kotlin online submissions for Number Complement.
Memory Usage: 30.9 MB, less than 100.00% of Kotlin online submissions for Number Complement.

First, we have to find the first 2^n - 1 which is higher than the input number.

For example, if input is 5, the first 2^n-1 would be 7. In binary, 5 is 101 and 7 would be 111. Next, we apply exclusive OR to them to get the 1’s complement.