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");
     }

 }