백준 10799번 쇠막대기 [ Java ]

10799번: 쇠막대기

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.*;

public class Main {
    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        Stack<Integer> stack = new Stack<>();
        String[] input = br.readLine().split("");
        int sum = 0;
        for (int i=0; i<input.length; i++){
            if (input[i].equals("("))
                stack.push(i);
            else{
                if (stack.peek() == i-1){
                    stack.pop();
                    sum += stack.size();
                }
                else{
                    stack.pop();
                    sum++;
                }
            }

        }
        System.out.print(sum);
    }
}