import java.util.*;

public class Main {
    public int solution(int[][] arr, int[] arr2){
        Stack<Integer> stack = new Stack<>();
        int cnt = 0;
        stack.push(0);
        for(int x : arr2){ // 1 5 3 5 1 2 1 4
            for(int i = 0; i < arr2.length; i++){ // 01 11 21 31 41
                if(arr[i][x] > 0){
                    int a = arr[i][x];
                    if(a  == stack.peek()){
                        stack.pop();
                        cnt++;
                    }
                    else
                        stack.push(a);
                    arr[i][x] = 0;
                    break;
                }
            }
        }
        return cnt * 2;
    }
    public static void main(String[] args) {
        Main t = new Main();
        Scanner kb = new Scanner(System.in);
        int n = kb.nextInt();
        int[][] arr = new int[n][n];
        for(int i =0; i < n; i++){
            for(int j = 0; j < n; j++) {
                arr[i][j] = kb.nextInt();
            }
        }
        int m = kb.nextInt();
        int[] arr2 = new int[m];
        for(int i = 0; i < m; m++){
            arr2[i] = kb.nextInt() - 1;
        }

        System.out.println(t.solution(arr, arr2));
    }
}

이렇게 코드를 작성해보았는데 런타임 에러가 뜨네요 ㅠㅠ 코드에
어느 부분이 문제가 있는지 잚 모르겠어서 질문 남깁니다!


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