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>
#define fi first
#define se second
#define endl "\n"
#define ii pair<int, int>
using namespace std;
const int N = 510, mod = 1e9 + 7;
int l[N], r[N], a[N], b[N], cnt[N << 1], inv[N], f[2][N << 1][N];
int power(int a, int p) {
if (!p) return 1;
int tmp = power(a, p >> 1);
tmp = 1LL * tmp * tmp % mod;
if (p % 2) return 1LL * tmp * a % mod;
return tmp;
}
void add(int &a, int b) {
a += b;
if (a >= mod) a -= mod;
}
int main() {
cin.tie(0) -> sync_with_stdio(0);
int n; cin >> n;
vector<int> rrh;
for(int i = 1; i <= n; i++) {
cin >> l[i] >> r[i];
rrh.push_back(l[i] - 1);
rrh.push_back(r[i]);
}
sort(rrh.begin(), rrh.end());
rrh.resize(unique(rrh.begin(), rrh.end()) - rrh.begin());
for(int i = 1; i <= n; i++) {
a[i] = upper_bound(rrh.begin(), rrh.end(), l[i] - 1) - rrh.begin();
b[i] = upper_bound(rrh.begin(), rrh.end(), r[i]) - rrh.begin();
// cout << a[i] << " " << b[i] << endl;
}
for(int i = 1; i < rrh.size(); i++) cnt[i + 1] = rrh[i] - rrh[i - 1];
// for(int i = 1; i <= rrh.size(); i++) cout << cnt[i] << " ";
for(int i = 2; i <= n; i++) inv[i] = power(i, mod - 2);
int m = rrh.size();
bool cur = 1;
for(int i = 1; i <= n; i++) {
bool pre = cur;
cur ^= 1;
for(int j = 1; j <= m; j++) for(int k = 0; k <= i; k++) f[cur][j][k] = f[pre][j][k];
int prefix = 1;
for(int j = 1; j <= a[i]; j++) for(int k = 0; k <= min(cnt[j], i); k++) add(prefix, f[pre][j][k]);
for(int j = a[i] + 1; j <= b[i]; j++) {
add(f[cur][j][1], 1LL * prefix * cnt[j] % mod);
add(prefix, f[pre][j][1]);
for(int k = 2; k <= i; k++) {
add(f[cur][j][k], 1LL * f[pre][j][k - 1] * (cnt[j] - k + 1) % mod * inv[k] % mod);
add(prefix, f[pre][j][k]);
}
}
}
int res = 0;
for(int j = 2; j <= m; j++) for(int k = 1; k <= n; k++) {
add(res, f[cur][j][k]);
}
cout << res;
}
Compilation message (stderr)
boat.cpp: In function 'int main()':
boat.cpp:38:22: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
38 | for(int i = 1; i < rrh.size(); i++) cnt[i + 1] = rrh[i] - rrh[i - 1];
| ~~^~~~~~~~~~~~
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