买鸡蛋问题

 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