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;
#define rep(i, n) for(int i = 1; (i) <= (n); ++i)
#define forn(i, l, r) for(int i = (l); i <= (r); ++i)
#define ford(i, r, l) for(int i = (r); i >= (l); --i)
#define FOR(i, n) for(int i = 0; i < (n); ++i)
#define FORD(i, n) for(int i = ((n) - 1); i >= 0; --i)
#define fi first
#define se second
#define pii pair<int, int>
#define pll pair<ll, ll>
#define pb push_back
#define endl "\n"
#define task "boat"
#define sz(a) int(a.size())
#define C(x, y) make_pair(x, y)
#define all(a) (a).begin(), (a).end()
#define bit(i, mask) (mask >> i & 1)
template<typename T> bool maximize(T &res, const T &val) { if (res < val){ res = val; return true; }; return false; }
template<typename T> bool minimize(T &res, const T &val) { if (res > val){ res = val; return true; }; return false; }
inline int readInt() {char c;while(c=getchar(),c!='-'&&(c<'0'||c>'9'));bool sign=(c=='-');if(sign)c=getchar();int n=c-'0';while(c=getchar(),c>='0'&&c<='9')n=10*n+c-'0';return(!sign)?n:-n;}
inline ll readLong() {char c;while(c=getchar(),c!='-'&&(c<'0'||c>'9'));bool sign=(c=='-');if(sign)c=getchar();ll n=c-'0';while(c=getchar(),c>='0'&&c<='9')n=10*n+c-'0';return(!sign)?n:-n;}
inline string readString() {char c;while(c=getchar(),c==' '||c=='\n'||c=='\t');string s({c});while(c=getchar(),c!=EOF&&c!=' '&&c!='\n'&&c!='\t')s+=c;return s;}
const int N = 1e3 + 10;
const int M = 1e3 + 3;
const int N1 = 2e3 + 10;
const int K = 1e2 + 1;
const int MOD = 1e9 + 7;
const int INF = 0x3f3f3f3f;
const ll LINF = 1e17 + 2;
const int block_size = 500;
const int LOG = 40;
const int offset = N;
const int LIM = 11 ;
const int AL = 26;
int add(int x, int y)
{
x += y;
if(x >= MOD) x -= MOD;
if(x < 0) x += MOD;
return x;
}
int mul(int x, int y)
{
return 1ll * x * y % MOD;
}
int n;
int a[N], b[N];
int C[N][N];
int comb[N], inv[N];
int dp[N][N];
vector<int> zip;
void solve()
{
cin >> n;
rep(i, n)
{
cin >> a[i] >> b[i];
zip.pb(a[i]);
zip.pb(b[i] + 1);
}
sort(all(zip));
zip.resize(unique(all(zip)) - zip.begin());
// rep(i, n) a[i] = upper_bound(all(zip), a[i]) - zip.begin();
// rep(i, n) b[i] = upper_bound(all(zip), b[i]) - zip.begin();
int m = sz(zip);
dp[0][0] = 1;
inv[0] = inv[1] = 1;
forn(i, 2, 2 * n) inv[i] = add(MOD, -mul(inv[MOD % i], MOD / i));
forn(i, 0, m - 1)
{
int l, r;
l = zip[i], r = i == m - 1 ? zip[i] : zip[i + 1];
comb[0] = 1;
forn(k, 1, n) comb[k] = mul(comb[k - 1], mul(inv[k], (r - l + k - 1)));
forn(j, 0, n)
{
dp[i + 1][j] = add(dp[i + 1][j], dp[i][j]);
int cnt = 0, cur = 1;
forn(k, j + 1, n)
{
if(a[k] <= l && b[k] >= r - 1)
{
dp[i + 1][k] = add(dp[i + 1][k], mul(dp[i][j], comb[++cnt]));
}
}
}
}
int res = 0;
forn(i, 1, n) res = add(res, dp[m][i]);
cout << res << endl;
}
signed main()
{
ios_base::sync_with_stdio(0);
cin.tie(0); cout.tie(0);
int TC = 1;
if(fopen(task".inp", "r"))
{
freopen(task".inp", "r", stdin);
freopen(task".out", "w", stdout);
}
while(TC--)
{
solve();
cout << endl;
}
return 0;
}
Compilation message (stderr)
boat.cpp: In function 'void solve()':
boat.cpp:98:26: warning: unused variable 'cur' [-Wunused-variable]
98 | int cnt = 0, cur = 1;
| ^~~
boat.cpp: In function 'int main()':
boat.cpp:124:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
124 | freopen(task".inp", "r", stdin);
| ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
boat.cpp:125:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
125 | freopen(task".out", "w", stdout);
| ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~
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