买鸡蛋问题

问题描述：超市有4种包装的鸡蛋，分别是3个一盒，6个一盒，9个一盒和20个一盒。问顾客要买N个鸡蛋时，所有的组合方案。(Morgen
Stanley 2014 Intern).

 1 void BuyeggsCore(vector<const int> &coins, const int target, int sum, int i, vector<int> &count, vector<vector<int>> &ret) {

 2     if (i >= 4) return;

 3     int left_value = target - sum;

 4     for (int j = 0; j * coins[i] <= left_value; ++j) {

 5         sum = target - left_value + j * coins[i];

 6         count[i] = j;

 7         if (sum == target) {

 8             ret.push_back(count);

 9         }

10         else if (sum < target) {

11             BuyeggsCore(coins, target, sum, i + 1, count, ret);

12         }

13     }

14 }

15

16 vector<vector<int>> BuyEggs(vector<const int> &coins, const int target) {

17     vector<vector<int>> ret;

18     vector<int> count;

19     count.resize(coins.size());

20     BuyeggsCore(coins, target, 0, 0, count, ret);

21     return ret;

22 }

23  

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