I really liked the solution to this problem as the code is extremely short. Thanks to Kotlin’s built-in operators.

```
class Solution {
fun heightChecker(heights: IntArray): Int {
return heights
.sorted()
.mapIndexed { index, i -> if(heights[index] != i) 1 else 0 }
.sum()
}
}
```

First, we sort the heights into ascending order then compare each item with the old values and check which of them flipped. Return 1 or 0 accordingly. Finally, the mapIndexed operator will give us a series of 1’s and 0’s and all that is left to do is to compute their sum.

```
Runtime: 176 ms, faster than 37.14% of Kotlin online submissions for Height Checker.
Memory Usage: 35.9 MB, less than 100.00% of Kotlin online submissions for Height Checker.
```