| # | Time | Username | Problem | Language | Result | Execution time | Memory |
|---|---|---|---|---|---|---|---|
| 40721 | ssnsarang2023 | Boat (APIO16_boat) | C++14 | 0 ms | 0 KiB |
This submission is migrated from previous version of oj.uz, which used different machine for grading. This submission may have different result if resubmitted.
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> ii;
#define SZ(x) ((int)x.size())
const int mod = (int)1e9+7;
const int N = 505;
int n, f[N], g[N], ftmp[N], gtmp[N], a[N], b[N], inv[N];
int choose[N][N], nCk[N]. nCk2[N], choose1[N][N], choose2[N][N];
vector<int> c, g[2*N];
int mul(int x, int y) {
return (int)((ll)x * (ll)y % (ll)mod);
}
void add(int &x, int y) {
x += y, x %= mod;
if (x < 0) x += mod;
}
int fast_pw(int x, int y) {
if (y == 1) return x % mod;
if (y == 0) return 1;
int t = fast_pw(x, y >> 1);
t = mul(t, t);
if (y & 1) t = mul(t, x);
return t;
}
int main() {
scanf("%d", &n);
for (int i = 1; i <= n; ++i) {
scanf("%d%d", &a[i], &b[i]);
c.push_back(a[i]);
c.push_back(b[i]);
}
sort(c.begin(), c.end());
c.resize(distance(c.begin(), unique(c.begin(), c.end())));
for (int i = 0; i <= n; ++i) choose[i][i] = choose[i][0] = 1;
inv[0] = 1;
for (int i = 1; i <= n; ++i) {
int lo = lower_bound(c.begin(), c.end(), a[i]) - c.begin();
int hi = lower_bound(c.begin(), c.end(), b[i]) - c.begin();
for (int j = lo; j <= hi; ++j) g[j].push_back(i);
for (int j = 1; j < i; ++j) choose[i][j] = (choose[i - 1][j] + choose[i][j - 1]) % mod;
inv[i] = mul(inv[i - 1], fast_pw(i, mod - 2));
}
for (int i = 0; i < SZ(c) - 1; ++i) {
vector<int> tmp;
for (int j = 0; j < SZ(g[i]); ++j) {
if (b[g[i][j]] == c[i]) ftmp[g[i][j]] = gtmp[g[i][j]] = g[g[i][j] - 1];
else tmp.push_back(g[i][j]);
for (int j = 1; j <= n; ++j) add(gtmp[j], gtmp[j - 1]);
int total = c[i + 1] - c[i], tmp_mul1 = 1, tmp_mul2 = 1;
for (int j = 1; j <= min(total, SZ(tmp)); ++j) {
tmp_mul1 = mul(tmp_mul1, total - j + 1);
tmp_mul2 = mul(tmp_mul2, total - j);
nCk[j] = mul(tmp_mul1, inv[j]);
nCk2[j] = mul(tmp_mul2, inv[j]);
}
for (int j = 0; j <= min(total, SZ(tmp)) - 2; ++j) {
for (int k = 0; k <= j; ++k) {
choose1[i][j] = mul(choose[i][j], nCk[j + 2]);
choose2[i][j] = mul(choose[i][j], nCk2[j + 2]);
add(choose1[i][j], choose1[i][j - 1]);
add(choose2[i][j], choose2[i][j - 1]);
}
}
for (int j = SZ(tmp) - 1; j >= 0; --j) {
int id = tmp[j];
ftmp[id] = (f[tmp[id]] + mul(nCk[1], g[id - 1])) % mod;
if (total > 1 && j > 0) {
for (int k = j - 1; k >= 0; --k) {
int mid = j - k - 1, id2 = tmp[k];
add(ftmp[id], mul(g[id2 - 1], choose1[mid][min(mid, total - 2)]));
if (total > 2) add(ftmp[id], mul(gtmp[id2 - 1], choose2[mid][min(mid, total - 3)]));
}
}
}
for (int i = 1; i <= n; ++i) {
add(f[i], ftmp[i]);
g[i] = (g[i - 1] + f[i]) % mod;
}
}
printf("%lld", g[n]);
return 0;
}