BZOJ2154 Crash的数字表格

昨天看了iwtwiioi的推导感觉很神！

今天想写结果又忘了怎么推的啦。。。233

 

 1 /**************************************************************
 2     Problem: 2154
 3     User: rausen
 4     Language: C++
 5     Result: Accepted
 6     Time:5124 ms
 7     Memory:127760 kb
 8 ****************************************************************/
 9  
10 #include <cstdio>
11 #include <algorithm>
12  
13 using namespace std;
14 typedef long long ll;
15  
16 const int N = 1e7 + 5;
17 const ll mod = 20101009;
18  
19 int n, m;
20 int p[N], cnt;
21 bool vis[N];
22 ll g[N];
23  
24 void get_g(int N) {
25   int i, j, k;
26   g[1] = 1;
27   for (i = 2; i <= N; ++i) {
28     if (!vis[i]) p[++cnt] = i, g[i] = 1 - i;
29     for (j = 1; j <= cnt; ++j) {
30       if ((k = i * p[j]) > N) break;
31       vis[k] = 1;
32       if (i % p[j] == 0) {
33     g[k] = g[i];
34     break;
35       }
36       g[k] = g[i] * (1 - p[j]);
37     }
38   }
39   for (i = 2; i <= N; ++i) g[i] *= i;
40   for (i = 1; i <= N; ++i)
41     (g[i] += g[i - 1]) %= mod;
42 }
43  
44 ll calc(int n, int m) {
45   int i, j;
46   ll t1, t2, res = 0;
47   for (i = 1, j = 0; i <= n; i = j + 1) {
48     j = min(n / (n / i), m / (m / i));
49     t1 = (1ll * (n / i) * (n / i + 1) / 2) % mod;
50     t2 = (1ll * (m / i) * (m / i + 1) / 2) % mod;
51     (res += ((g[j] - g[i - 1]) * ((t1 * t2) % mod)) % mod) %= mod;
52   }
53   return (res % mod + mod) % mod;
54 }
55  
56 int main() {
57   int i, T;
58   scanf("%d%d", &n, &m);
59   if (n > m) swap(n, m);
60   get_g(m);
61   printf("%lld\n", calc(n, m));
62   return 0;
63 }
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posted on 2015-02-14 21:25  Xs酱~  阅读(204)  评论(0)  编辑  收藏  举报