G面经prepare: BuyGoods

给你一部分钱和一些不同价钱的商品，如何在最多买K件商品的情况下尽可能多的花掉手里的钱。
举例：口袋里的钱数： 10;   K=2     产品价格: [3, 6, 8, 7, 9]   输出 3, 7

Backtracking:

 package BuyGoods;
 import java.util.*;

 public class Solution {
     static int minRemain = 0;

     public ArrayList<Integer> optimize(int money, int[] prices, int k) {
         ArrayList<Integer> result = new ArrayList<Integer>();
         ArrayList<Integer> path = new ArrayList<Integer>();
         minRemain = money;
         helper(result, path, money, prices, 0, k);
         return result;
     }

     public void helper(ArrayList<Integer> result, ArrayList<Integer> path, int remain, int[] prices, int pos, int times) {
         if (remain < 0 || times<0) return;
         if (remain < minRemain) {
             minRemain = remain;
             result.clear();
             result.addAll(path);
         }
         for (int i=pos; i<prices.length; i++) {
             path.add(prices[i]);
             helper(result, path, remain-prices[i], prices, i+1, times-1);
             path.remove(path.size()-1);
         }

     }

     /**
      * @param args
      */
     public static void main(String[] args) {
         // TODO Auto-generated method stub
         Solution sol = new Solution();
         ArrayList<Integer> result = sol.optimize(10, new int[]{7,8,1,6,9}, 3);
         System.out.println(result);
     }

 }