G面经prepare: X-Straight

Define “X-Straight” as X cards with consecutive numbers (X >= 3). Determine if the deck can be fully divided into sets of “X-Straight”.
Example: 1, 2, 3, 4, 4, 5, 6 -> True

Backtracking:

package Straight;
import java.util.*;

public class Solution2 {
    HashMap<Integer, Integer> map = new HashMap<Integer, Integer>();
    public boolean determine(int[] arr) {
        for (int elem : arr) {
            if (!map.containsKey(elem)) {
                map.put(elem, 1);
            }
            else map.put(elem, map.get(elem)+1);
        }
        return helper(arr, 0);
    }
    
    public boolean helper(int[] arr, int pos) {
        if (pos == arr.length) return true;
        int cur = arr[pos];
        for (int k=3; k<map.keySet().size(); k++) {
            HashMap<Integer, Integer> copy = new HashMap<Integer, Integer>(map);
            for (int i=cur; i<cur+k; i++) {
                if (!map.containsKey(i)) return false;
                if (map.get(i) == 0) return false;
                map.put(i, map.get(i)-1);
            }
            while (pos<arr.length && map.get(arr[pos]) == 0) pos++;
            if (helper(arr, pos))
                return true;
            map = copy;
        }
        return false;
        
    }

    /**
     * @param args
     */
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Solution2 sol = new Solution2();
        boolean res = sol.determine(new int[]{1,2,3,2,3,4,8,9,10,6});
        if (res) System.out.println("true");
        else System.out.println("false");
    }

}