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奖励最顶尖的 k 名学生(哈希表+排序)

用哈希表对所有的positive与negative词条进行映射，然后遍历求解。tip：常用的分割字符串的操作：1.stringstream配合getline() [格式buf, string, char]2.string.find()[find未找到目标会返回npos]配合string.substr()

class Solution {
public:
    vector<int> topStudents(vector<string>& positive_feedback, vector<string>& negative_feedback, vector<string>& report, vector<int>& student_id, int k) {
        unordered_set<string> pos, neg;
        for (auto& s : positive_feedback) pos.insert(s);
        for (auto& s : negative_feedback) neg.insert(s);
        vector<pair<int, int>> arr;
        int n = student_id.size();
        for (int i = 0; i < n; ++i) {
            stringstream ss;
            ss << report[i];
            string tmp;
            int res = 0;
            while (getline(ss, tmp, ' ')) {
                if (pos.count(tmp)) res += 3; 
                else if (neg.count(tmp)) res--;
            }
            arr.push_back({-res, student_id[i]});
        }
        sort(arr.begin(), arr.end());
        vector<int> ans(k);
        for (int i = 0; i < k; ++i) ans[i] = arr[i].second;
        return ans;
    }
};