题解 | #牛群喂食#

class Solution {
public:
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @param candidates int整型vector 
     * @param target int整型 
     * @return int整型vector<vector<>>
     */
    void backtrace(vector<int>& candidates, int sum, vector<int>&path, vector<vector<int>>& ans, int target, int start) {
        if (sum == target) {
            ans.push_back(path);
            return;
        }
        for (int i = start; i < candidates.size(); i++) {
            if (sum + candidates[i] > target) {
                return;
            }
            path.push_back(candidates[i]);
            backtrace(candidates, sum+candidates[i], path, ans, target, i);
            path.pop_back();
        }
    }
    vector<vector<int> > cowCombinationSum(vector<int>& candidates, int target) {
        // write code here
        vector<int> path;
        vector<vector<int>> ans;
        int sum = 0;
        backtrace(candidates, sum, path, ans, target, 0);
        return ans;
    }
};