codeforces 492C. Vanya and Exams 解题报告

 1 #include <iostream>
 2 #include <cstdio>
 3 #include <cstdlib>
 4 #include <cstring>
 5 #include <algorithm>
 6 using namespace std;
 7 
 8 typedef __int64 LL;
 9 const int maxn = 1e5 + 5;
10 struct node
11 {
12     LL a, b;
13 }exam[maxn];
14 
15 LL cmp(node x, node y)
16 {
17     if (x.b == y.b)
18         return x.a < y.a;
19     return x.b < y.b;
20 }
21 
22 int main()
23 {
24     #ifndef ONLINE_JUDGE
25         freopen("in.txt", "r", stdin);
26     #endif // ONLINE_JUDGE
27     LL n, r, avg;
28     LL has, need, needed;
29 
30     while (scanf("%I64d%I64d%I64d", &n, &r, &avg) != EOF)
31     {
32         has = 0;
33         for (__int64 i = 0; i < n; i++)
34         {
35             scanf("%I64d%I64d", &exam[i].a, &exam[i].b);
36             has += exam[i].a;
37         }
38 
39         sort(exam, exam+n, cmp);
40         LL needed = 1ll * avg * n;
41         LL need = 1ll*needed - 1ll*has;
42         if (need <= 0)
43             printf("0\n");
44         else
45         {
46             LL ans = 0;
47             for (LL i = 0; i < n && need > 0; i++)
48             {
49                 if ((r-exam[i].a) <= need)
50                 {
51                     ans += (r-exam[i].a) * exam[i].b;
52                     need -= r-exam[i].a;
53                 }
54                 else
55                 {
56                     ans += need * exam[i].b;
57                     need -= need;
58                 }
59             }
60             printf("%I64d\n", ans);
61         }
62     }
63     return 0;
64 }