Marc Lester Tan

For this problem, the idea is to swap each digit with their corresponding 180-degree values and use Integer.parseInt to verify if it’s still a valid number. If yes, check also if it’s not equal to the original number as this may also affect the validity of the number.

class Solution {
    
    fun isGood(num: Int): Boolean {
        val s = num.toString()
        val builder = StringBuilder()
        val newValue = s.map {
            when {
                it == '0' || it == '1' || it == '8' -> it
                it == '2' -> '5'
                it == '5' -> '2'
                it == '6' -> '9'
                it == '9' -> '6'
                else -> return false
            }
        }.joinToString("")
        
        return try{
            Integer.parseInt(newValue) != num
        }catch(e: Exception){
            false
        }
    }
    
    fun rotatedDigits(N: Int): Int {
        var ctr = 0
        (2..N).forEach { 
            if(isGood(it)) {
                ctr++
            }
        }
        
        return ctr
    }
}

Runtime: 256 ms, faster than 23.08% of Kotlin online submissions for Rotated Digits.
Memory Usage: 39.1 MB, less than 100.00% of Kotlin online submissions for Rotated Digits.