As I’ve mentioned before, I really enjoy solving problems involving bit manipulation and this is one of the many problems that are fun to solve with.

```
class Solution {
fun readBinaryWatch(num: Int): List<String> {
val times = mutableListOf<String>()
(0..11).forEach { hour ->
val hourBits = Integer.bitCount(hour)
// for every possible hours
if(hourBits <= num) {
// find out every possible minutes
(0..59).forEach { minute ->
val minBits = Integer.bitCount(minute)
// num - hourBits calculates the remaining LEDs that can be turned on for the minute LEDs
if(minBits == num - hourBits) {
times.add("$hour:${if(minute < 10) "0$minute" else minute}")
}
}
}
}
return times.toList()
}
}
```

```
Runtime: 152 ms, faster than 100.00% of Kotlin online submissions for Binary Watch.
Memory Usage: 33.5 MB, less than 100.00% of Kotlin online submissions for Binary Watch.
```

Time complexity is O( 12 x 60 ) or O(1)