import java.util.*;

public class Main
{
static class city
{
int start_loc = 0;
int reach_loc = 0;
int gap = 0;

city() {}
}

public static void main(String[] args) 
{
    Scanner s = new Scanner(System.in);

    int testcase = Integer.parseInt(s.nextLine());

    if(testcase < 0 || testcase > 50)
        return;

    for(int test = 0 ; test < testcase ; test++)
    {
        int count = 0;
        List<Integer> sign_loc = new ArrayList<Integer>();
        String[] citynum_location = s.nextLine().split(" ");

        int citynum = Integer.parseInt(citynum_location[0]);
        if(citynum < 1 || citynum > 5000) return;

        int location = Integer.parseInt(citynum_location[1]);
        if(location < 1 || location > (Math.pow(2,31) -1)) return;

        String[] value = new String[citynum];
        city[] temp = new city[citynum];

        for(int i=0;i<citynum;i++)
        {
            value = s.nextLine().split(" ");
            temp[i] = new city();
            temp[i].reach_loc = Integer.parseInt(value[0]);
            temp[i].start_loc = Integer.parseInt(value[1]);
            temp[i].gap = Integer.parseInt(value[2]);
            if(temp[i].reach_loc < 1 || temp[i].reach_loc > 8030000 || temp[i].start_loc < 1 || temp[i].start_loc > 8030000 
                    || temp[i].gap < 1 || temp[i].gap > 8030000) return;
        }
        //입력완료
        for(int i=0;i<citynum;i++)
        {
            int current = temp[i].reach_loc - temp[i].start_loc;
            while(current <= temp[i].reach_loc)
            {
                sign_loc.add(current);
                current += temp[i].gap;
            }       
        }

        sign_loc.sort(null);

        System.out.println(sign_loc.get(location-1));
    }
}

}

예제 입력햇을때 정답은 나오고 과정은 맞는것같은데 메모리와 속도가 문제인거 같네요... sign_loc.sort()부분에서 엄청난 시간을 잡아먹는것 같고 메모리도 잡아 먹는것 같구요... 어떤 부분을 수정해야 맞을까요? ㅠㅠ