2512. Reward Top K Students

Problem

You are given two string arrays positive_feedback and negative_feedback, containing the words denoting positive and negative feedback, respectively. Note that no word is both positive and negative.

Initially every student has 0 points. Each positive word in a feedback report increases the points of a student by 3, whereas each negative word decreases the points by 1.

You are given n feedback reports, represented by a 0-indexed string array report and a 0-indexed integer array student_id, where student_id[i] represents the ID of the student who has received the feedback report report[i]. The ID of each student is unique.

Given an integer k, return **the top *k* students after ranking them in non-increasing order by their points**. In case more than one student has the same points, the one with the lower ID ranks higher.

  Example 1:

Input: positive_feedback = ["smart","brilliant","studious"], negative_feedback = ["not"], report = ["this student is studious","the student is smart"], student_id = [1,2], k = 2
Output: [1,2]
Explanation: 
Both the students have 1 positive feedback and 3 points but since student 1 has a lower ID he ranks higher.

Example 2:

Input: positive_feedback = ["smart","brilliant","studious"], negative_feedback = ["not"], report = ["this student is not studious","the student is smart"], student_id = [1,2], k = 2
Output: [2,1]
Explanation: 
- The student with ID 1 has 1 positive feedback and 1 negative feedback, so he has 3-1=2 points. 
- The student with ID 2 has 1 positive feedback, so he has 3 points. 
Since student 2 has more points, [2,1] is returned.

  Constraints:

• 1 <= positive_feedback.length, negative_feedback.length <= 104

• 1 <= positive_feedback[i].length, negative_feedback[j].length <= 100

• Both positive_feedback[i] and negative_feedback[j] consists of lowercase English letters.

• No word is present in both positive_feedback and negative_feedback.

• n == report.length == student_id.length

• 1 <= n <= 104

• report[i] consists of lowercase English letters and spaces ' '.

• There is a single space between consecutive words of report[i].

• 1 <= report[i].length <= 100

• 1 <= student_id[i] <= 109

• All the values of student_id[i] are unique.

• 1 <= k <= n

Solution (Java)

class Solution {
    public List<Integer> topStudents(String[] positive_feedback, String[] negative_feedback, String[] report, int[] student_id, int k) {
        List<Integer> res = new ArrayList<>();
        Set<String> pos = new HashSet<>(List.of(positive_feedback));
        Set<String> neg = new HashSet<>(List.of(negative_feedback));
        int n = report.length;
        int[][] rank = new int[n][2];
        // System.out.println(n);
        for (int i = 0; i < n; i++) {
            String rep = report[i];
            rank[i][0]=student_id[i];
            String[] strs=rep.split(" ");
            for(String s:strs){
                if(pos.contains(s)){
                    rank[i][1]+=3;
                }
                if(neg.contains(s)){
                    rank[i][1]-=1;
                }
            }
        }
        Arrays.sort(rank,(a,b)->{
            if(a[1]==b[1]){
                return a[0]-b[0];
            }
            return b[1]-a[1];
        });

        for(int i=0;i<k;i++){
            res.add(rank[i][0]);
        }
        return res;
    }
}

Explain:

nope.

Complexity:

• Time complexity : O(n).
• Space complexity : O(n).