题解 | #奖学金#

import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        while (sc.hasNext()) {
            int n = sc.nextInt();
            int r = sc.nextInt();
            int avg = sc.nextInt();
            int[][] arr = new int[n][2];
            for (int i = 0; i < n; i++) {
                arr[i][0] = sc.nextInt();
                arr[i][1] = sc.nextInt();
            }
            long res = result(n, r, avg, arr);
            System.out.println(res);
        }
        sc.close();
    }

    public static long result(long n, long r, long avg, int[][] arr) {
        Arrays.sort(arr, (o1, o2) -> (int) (o1[1] - o2[1]));
        long res = 0;//一共需复习时间
        long socre = n * avg;//n门课拿奖学金所需的分数
        int index=0;
        for (int[] num : arr) {
            socre -= num[0];//去除平时分，剩下的分数是复习所取得的
        }
        while(socre>0){
            if(socre>=r-arr[index][0]){
                res+=arr[index][1]*(r-arr[index][0]);
                socre-=r-arr[index][0];
                index++;
            }else{
                res+=arr[index][1]*(socre);
                socre=0;
            }
        }
        return res;
    }
}