Решение

class Solution {
    fun isValid(s: String): Boolean {
        val n = s.length
        if ((n and 1) == 1) return false
        val st = CharArray(n)
        var t = 0
        for (ch in s) {
            when (ch) {
                '(' -> st[t++] = ')'
                '[' -> st[t++] = ']'
                '{' -> st[t++] = '}'
                else -> if (t == 0 || st[--t] != ch) return false
            }
        }
        return t == 0
    }
}