How to implement a check for correct parentheses placement in a string using the Valid Parentheses problem on LeetCode?

To check the correctness of bracket placement in a string, a stack can be used. The idea is to iterate through the characters of the string and:

• If the character is an opening bracket (for example, '(', '{', '['), push it onto the stack.
• If the character is a closing bracket, check that the top element of the stack is the corresponding opening bracket. If yes, pop it from the stack; otherwise, the string is incorrect.

At the end, if the stack is empty, all brackets are correctly closed.

Example in Java/Kotlin:

fun isValid(s: String): Boolean {
    val stack = mutableListOf<Char>()
    val pairs = mapOf(')' to '(', ']' to '[', '}' to '{')

    for (char in s) {
        if (char in pairs.values) {
            stack.add(char)
        } else if (char in pairs.keys) {
            if (stack.isEmpty() || stack.removeAt(stack.size - 1) != pairs[char]) {
                return false
            }
        }
    }
    return stack.isEmpty()
}

This method efficiently checks the correctness of nesting and matching brackets.