HW3_brackets3

#include <cstdio>
#include <cstdlib>

int main()
{
    int n = 0, k = -1, fl = 0;
    scanf("%d", &n);
    char* arr = (char*)malloc(n+1);
    scanf("%s", arr);
    arr[n] = 0;
    char* stack = (char*)malloc(n);
    for (int i = 0; i < n; i++)
    {
        if (arr[i] == '(' || arr[i] == '[' || arr[i] == '{')
        {
            k++;
            stack[k] = arr[i];
        }
        else if (arr[i] == ')' || arr[i] == ']' || arr[i] == '}')
        {
            if (k == -1)
            {
                fl = 1;
                break;
            }
            if ((arr[i] == ')' && stack[k] == '(') || (arr[i] == ']' && stack[k] == '[') || (arr[i] == '}' && stack[k] == '{'))
                k--;
            else
            {
                fl = 1;
                break;
            }
        }
    }
    if (k != -1)
        fl = 1;
    if (fl == 0)
        printf("OK\n");
    else
        printf("ERROR\n");
    return 0;
}