BZOJ 4584: [Apio2016]赛艇

 1 #include<bits/stdc++.h>
 2 
 3 using namespace std;
 4 
 5 const long long INF = 1000000007;
 6 
 7 const int MAXN = 510;
 8 long long n, p, top, ans;
 9 long long inv[MAXN];
10 long long a[MAXN], b[MAXN], l[MAXN], r[MAXN]; 
11 long long h[MAXN + MAXN];
12 long long C[MAXN], g[MAXN];
13 map<long long, int> k;
14 
15 template <typename tn> void read (tn & a) {
16     tn x = 0, f = 1; char c = getchar();
17     while (c < ‘0‘ || c > ‘9‘) { if (c == ‘-‘) f = -1; c = getchar(); }
18     while (c >= ‘0‘ && c <= ‘9‘) { x = x * 10 + c - ‘0‘; c = getchar(); }
19     a = f == 1 ? x : -x;
20 }
21 
22 void get_inv() {
23     inv[1] = 1;
24     for (int i = 2; i <= n; ++i) {
25         inv[i] = - ( inv[INF % i] * (INF / i) ) % INF;
26         while (inv[i] < 0) inv[i] += INF;
27     }
28 }
29 
30 int main() {
31     read(n);
32     get_inv();
33     for (int i = 1; i <= n; ++i) {
34         read(a[i]);
35         read(b[i]);
36         ++b[i];
37         h[i + i - 1] = a[i];
38         h[i + i] = b[i];
39     }
40     sort(h + 1, h + 1 + n + n);
41     top = unique(h + 1, h + n + n + 1) - h - 1;
42     for (int i = 1; i <= top; ++i) {
43         k[h[i]] = i;
44     }
45     for (int i = 1; i <= n; ++i) {
46         l[i] = k[a[i]];
47         r[i] = k[b[i]];
48     }
49 //    cout << top << "\n";
50 //    for (int i = 1; i <= top; ++i) cout << h[i]<<" ";
51 //    for (int i = 1; i <= n; ++i) cout << l[i]<<" "<<r[i]<<"\n";
52     g[0] = 1;
53     for (int j = 1; j <= top; ++j) {
54         int L = h[j + 1] - h[j];
55         C[0] = 1;
56 //        cerr<<"j = "<<j<<"\n";
57         for (int i = 1; i <= n; ++i) {
58             C[i] = C[i - 1] * (L + i - 1) % INF * inv[i] % INF;
59 //            cerr<<i<<" "<<C[i]<<"\n";
60         }
61         for (int i = n; i > 0; --i) {
62             if (l[i] <= j && r[i] > j) {
63                 long long f = 0, m = 1, c = L;
64                 for (int p = i - 1; p >= 0; --p) {
65                     f = (f + c * g[p]) % INF;
66                     if (l[p] <= j && r[p] >= j + 1) {
67                         c = C[++m];
68                     }
69                 }
70                 g[i] = (g[i] + f) % INF;
71             }
72         }
73     }
74     for (int i = 1; i <= n; ++i) ans = (ans + g[i]) % INF;
75     printf("%lld\n", ans);
76     return 0;
77 }