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);
    }

}