Given a list of scores of different students, return the average score of each student's top five scores in the order of each student's id.
Each entry items[i] has items[i][0] the student's id, and items[i][1] the student's score. The average score is calculated using integer division.
Example 1:
Input: [[1,91],[1,92],[2,93],[2,97],[1,60],[2,77],[1,65],[1,87],[1,100],[2,100],[2,76]] Output: [[1,87],[2,88]] Explanation: The average of the student with id = 1 is 87. The average of the student with id = 2 is 88.6. But with integer division their average converts to 88.
思路：就是一个hashmap统计和priorityqueue统计top k
class Solution {
private class Node {
public int id;
public int average;
public Node(int id, int average) {
this.id = id;
this.average = average;
}
}
private class NodeComparator implements Comparator<Node> {
@Override
public int compare(Node a, Node b) {
return a.id - b.id;
}
}
public int[][] highFive(int[][] items) {
if(items == null || items.length == 0 || items[0].length == 0) {
return new int[0][0];
}
HashMap<Integer, PriorityQueue<Integer>> hashmap = new HashMap<>();
for(int i = 0; i < items.length; i++) {
int id = items[i][0];
int score = items[i][1];
hashmap.putIfAbsent(id, new PriorityQueue<Integer>());
if(hashmap.get(id).size() < 5) {
hashmap.get(id).add(score);
} else{
if(hashmap.get(id).peek() < score) {
hashmap.get(id).poll();
hashmap.get(id).add(score);
}
}
}
List<Node> list = new ArrayList<Node>();
int index = 0;
for(Integer key: hashmap.keySet()) {
int average = calculate(hashmap.get(key));
list.add(new Node(key, average));
}
Collections.sort(list, new NodeComparator());
int[][] result = new int[list.size()][2];
for(int i = 0; i < list.size(); i++) {
result[i][0] = list.get(i).id;
result[i][1] = list.get(i).average;
}
return result;
}
private int calculate(PriorityQueue<Integer> pq) {
int sum = 0;
while(!pq.isEmpty()) {
Integer integer = pq.poll();
sum += integer.intValue();
}
return sum / 5;
}
}