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;
#define ii pair <int, int>
#define app push_back
#define all(a) a.begin(), a.end()
#define bp __builtin_popcount
#define ll long long
#define mp make_pair
#define f first
#define s second
#define Time (double)clock()/CLOCKS_PER_SEC
const int N = 2e6 + 7, MOD = 1000 * 1000 * 1000 + 7;
int l[N], r[N], mn[N << 2], mx[N << 2], num[N], numr[N];
bool ans[N], used[N];
void relax(int v) {
mx[v] = max(mx[v * 2 + 1], mx[v * 2 + 2]);
}
void build(int v, int tl, int tr) {
if (tl == tr) {
if (num[tl])
mx[v] = r[num[tl]];
return;
}
int tm = (tl + tr) >> 1;
build(v * 2 + 1, tl, tm); build(v * 2 + 2, tm + 1, tr);
relax(v);
}
void relax_left(int v) {
mn[v] = min(mn[v * 2 + 1], mn[v * 2 + 2]);
}
void build_left(int v, int tl, int tr) {
if (tl == tr) {
if (numr[tl])
mn[v] = l[numr[tl]];
else
mn[v] = N;
return;
}
int tm = (tl + tr) >> 1;
build_left(v * 2 + 1, tl, tm); build_left(v * 2 + 2, tm + 1, tr);
relax_left(v);
}
queue <int> q;
void color(int v, int tl, int tr, int l, int r, int x, bool c) {
if (tr < l || r < tl || mx[v] <= x)
return;
if (tl == tr) {
int i = num[tl];
if (!used[i]) {
used[i] = 1;
ans[i] = c;
q.push(i);
}
mx[v] = 0;
return;
}
int tm = (tl + tr) >> 1;
color(v * 2 + 1, tl, tm, l, r, x, c);
color(v * 2 + 2, tm + 1, tr, l, r, x, c);
relax(v);
}
void color_left(int v, int tl, int tr, int l, int r, int x, bool c) {
if (tr < l || r < tl || mn[v] >= x)
return;
if (tl == tr) {
int i = numr[tl];
if (!used[i]) {
used[i] = 1;
ans[i] = c;
q.push(i);
}
mn[v] = N;
return;
}
int tm = (tl + tr) >> 1;
color_left(v * 2 + 1, tl, tm, l, r, x, c);
color_left(v * 2 + 2, tm + 1, tr, l, r, x, c);
relax_left(v);
}
void check(vector <ii> a) {
sort(all(a));
vector <int> r = {N};
for (auto e : a) {
while (r.back() < e.f)
r.pop_back();
if (r.back() < e.s) {
cout << 0 << endl;
exit(0);
}
r.app(e.s);
}
}
signed main() {
#ifdef HOME
freopen("input.txt", "r", stdin);
#else
#define endl '\n'
ios_base::sync_with_stdio(0); cin.tie(0);
#endif
int n;
cin >> n;
vector <ii> a;
vector <int> per;
for (int i = 1; i <= n; ++i) {
cin >> l[i] >> r[i];
num[l[i]] = i;
numr[r[i]] = i;
}
build(0, 1, N - 1);
build_left(0, 1, N - 1);
int ptr = 1, comp = 1;
while (1) {
while (ptr <= n && used[ptr])
++ptr;
if (ptr == n + 1)
break;
comp = (comp << 1) % MOD;
q.push(ptr);
used[ptr] = 1;
while (q.size()) {
int i = q.front(); q.pop();
color(0, 1, N - 1, l[i] + 1, r[i] - 1, r[i], ans[i] ^ 1);
color_left(0, 1, N - 1, l[i] + 1, r[i] - 1, l[i], ans[i] ^ 1);
}
}
vector <ii> t[2];
for (int i = 1; i <= n; ++i)
t[ans[i]].app(mp(l[i], r[i]));
for (int i = 0; i < 2; ++i)
check(t[i]);
cout << comp << endl;
}
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