TOJ1398 bfs混合dfs较慢

import java.io.File;
import java.io.FileNotFoundException;
import java.util.Scanner;

public class IsSquare2 {

static int len;static int avg;static boolean[] isV;static int[] seq;static int flag;public static void main(String[] args) throws FileNotFoundException {    // TODO Auto-generated method stub    @SuppressWarnings("resource")    Scanner sc = new Scanner(System.in);    sc = new Scanner(new File("files/issquare"));    int T = sc.nextInt();    for (int t = 0; t < T; t++) {        len = sc.nextInt();        avg = 0;        seq = new int[len];        isV = new boolean[len];        int max = 0;        for (int i = 0; i < len; i++) {            seq[i] = sc.nextInt();            avg += seq[i];            if (seq[i] > max)                max = seq[i];        }        if (avg % 4 != 0) {            System.out.println("no");        } else if (len == 4) {            if (seq[0] == seq[1] && seq[0] == seq[2] && seq[0] == seq[3])                System.out.println("yes");            else                System.out.println("no");        } else {            avg /= 4;            if (max > avg)                System.out.println("no");            else {                flag=0;                BFS(1, 1);                if (flag == 1)                    System.out.println("yes");                else                    System.out.println("no");            }        }    }}private static void BFS(int c, int sn) {    // TODO Auto-generated method stub    if (flag == 1)        return;    if (c == 5) {        flag = 1;        return;    }    for (int i = sn; i < len - 2; i++) {        int[] queue = new int[i];        dfs(0, -1, i, queue, 0, c);    }}private static void dfs(int s, int pre, int step, int[] q, int sum, int c) {    // TODO Auto-generated method stub    if (s == step) {        if (sum == avg) {            boolean[] tmpv = new boolean[len];            CopyOf(tmpv, isV);            for (int i = 0; i < step; i++) {                isV[q[i]] = true;            }            BFS(c + 1, step);            CopyOf(isV, tmpv);        }        return;    }    for (int i = pre + 1; i < len; i++) {        if (!isV[i]) {            q[s] = i;            sum += seq[i];            dfs(s + 1, i, step, q, sum, c);            if (flag == 1)                return;            sum -= seq[i];        }    }}private static void CopyOf(boolean[] v1, boolean[] v2) {    // TODO Auto-generated method stub    for (int i = 0; i < len; i++) {        v1[i] = v2[i];    }}

}

sample input:
10
20 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 161
10 15 4 1 11 3 2 8 8 8 20
5 20 30 20 30 24
7 6 2 1 7 3 8 9
6 1 2 10001 9999 10000 10001
20 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 30
4 1 1 1 1
9 1 7 2 6 4 4 3 2 3
5 5 5 3 2 5
20 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5
sample output:
no
yes
no
yes
yes
yes
yes
yes
yes
yes