Решение

class Solution {
    fun removeDuplicates(s: String): String {
        val n = s.length
        val st = CharArray(n)
        var top = 0
        var i = 0
        while (i < n) {
            val c = s[i]
            if (top > 0 && st[top - 1] == c) {
                top--
            } else {
                st[top++] = c
            }
            i++
        }
        return String(st, 0, top)
    }
}