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 nl '\n'
#ifdef LOCAL
#include "template/debug.hpp"
#else
#define dbg(...) ;
#define timer(...) ;
#endif
template <int md>
struct Modular {
int v;
constexpr Modular() : v(0) {}
template <typename T>
static inline int normalize(const T& x) {
int res = -md <= x && x < md ? static_cast<int>(x) : static_cast<int>(x % md);
return res + (res < 0) * md;
}
static constexpr int mod() {
return md;
}
template <typename U>
Modular(const U& x) : v(normalize(x)) {}
const int& operator()() const { return v; }
template <typename U>
explicit operator U() const {
return static_cast<U>(v);
}
using M = Modular;
constexpr static inline M _raw(int x) {
static_assert(x >= 0 && x < md);
M res;
res.v = x;
return res;
}
template <typename U>
friend std::enable_if_t<std::is_integral_v<U>, M> power(M b, U e) {
assert(e >= 0);
M ans = 1;
while (e) {
if (e & 1) ans *= b;
b *= b;
e >>= 1;
}
return ans;
}
M inv() const {
M res = power(*this, md - 2);
return res;
}
M& operator+=(const M& y) { return v += y.v, v -= (v >= md) * md, *this; }
M& operator-=(const M& y) { return v -= y.v, v += (v < 0) * md, *this; }
M& operator*=(const M& y) { return v = (int64_t) v * y.v % md, *this; }
M& operator/=(const M& y) { return *this *= y.inv(); }
M& operator++() { return *this += _raw(1); }
M& operator--() { return *this -= _raw(1); }
M operator++(int) {
M res(*this);
return *this += _raw(1), res;
}
M operator--(int) {
M res(*this);
return *this -= _raw(1), res;
}
M operator-() const { return M(-v); }
friend bool operator==(const M& x, const M& y) { return x.v == y.v; }
friend bool operator<(const M& x, const M& y) { return x.v < y.v; }
friend bool operator>(const M& x, const M& y) { return x.v > y.v; }
friend bool operator<=(const M& x, const M& y) { return x.v <= y.v; }
friend bool operator>=(const M& x, const M& y) { return x.v >= y.v; }
friend bool operator!=(const M& x, const M& y) { return x.v != y.v; }
template <typename Istream>
friend Istream& operator>>(Istream& is, M& y) {
int64_t x;
is >> x;
y.v = y.normalize(x);
return is;
}
template <typename Ostream>
friend Ostream& operator<<(Ostream& os, const M& y) {
return os << y.v;
}
friend M operator+(const M& x, const M& y) { return M(x) += y; }
friend M operator-(const M& x, const M& y) { return M(x) -= y; }
friend M operator*(const M& x, const M& y) { return M(x) *= y; }
friend M operator/(const M& x, const M& y) { return M(x) /= y; }
};
constexpr int md = 1e9 + 7;
using Mint = Modular<md>;
signed main() {
std::ios::sync_with_stdio(false);
std::cin.tie(nullptr);
int n;
std::cin >> n;
std::vector<int> a(n), b(n);
for (int i = 0; i < n; i++) std::cin >> a[i] >> b[i];
const int mxA = 10;
std::vector<Mint> dp(mxA);
dp[0] = 1;
for (int i = 0; i < n; i++) {
std::vector<Mint> ndp(mxA);
Mint sum = 0;
for (int j = 0; j < mxA; j++) {
ndp[j] = dp[j];
if (a[i] <= j && j <= b[i]) {
ndp[j] += sum;
}
sum += dp[j];
}
std::swap(dp, ndp);
dbg(dp);
}
std::cout << std::accumulate(dp.begin() + 1, dp.end(), Mint()) << nl;
}
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