Poj Solution 1250

http://poj.org/problem?id=1250

//* @author ������<hongxp11@163.com>
    import java.util.ArrayList;
import java.util.HashSet;
import java.util.Scanner;
import java.util.Set;

public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        while (true) {
            int num = in.nextInt();
            if (num == 0)
                break;
            String customers = in.next();
            int leftCustomer = 0;
            Set<Character> customerSet = new HashSet<Character>();
            for (int i = 0; i < customers.length(); i++) {
                int size = customerSet.size();
                if (size >= num) {
                    if (customerSet.contains(customers.charAt(i))) {
                        customerSet.remove(customers.charAt(i));
                        continue;
                    }
                    leftCustomer++;
                    int index = customers.indexOf(customers.charAt(i), i + 1);
                    if (index != -1)
                        customers = customers.substring(0, index)
                                + customers.substring(index + 1);
                } else {
                    if (customerSet.contains(customers.charAt(i))) {
                        customerSet.remove(customers.charAt(i));
                    } else
                        customerSet.add(customers.charAt(i));
                }
            }
            if (leftCustomer == 0)
                System.out.println("All customers tanned successfully.");
            else
                System.out.println(leftCustomer + " customer(s) walked away.");
        }
    }
}