#include <cctype>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <vector>
int nextInt() {
char ch;
while (!isdigit(ch = getchar())) {}
int res = ch - '0';
while (isdigit(ch = getchar())) res = 10 * res + ch - '0';
return res;
}
const int N = 2000000 + 10, MOD = 1000000007;
int n, a[N], b[N], c[N], id[N];
std::vector<int> adj[N];
void link(int a, int b) {
adj[a].push_back(b);
adj[b].push_back(a);
}
std::vector<int> pool[N];
void update(int p, int v) {
for (; p <= 2 * n; p += p & -p) pool[p].push_back(v);
}
void query(int p, int v) {
for (; p; p ^= p & -p) {
if (pool[p].empty()) continue;
int x = pool[p].back();
if (b[x] < a[v]) continue;
for (; !pool[p].empty(); pool[p].pop_back()) {
int u = pool[p].back();
if (b[u] >= a[v]) link(u, v);
}
pool[p].push_back(x);
}
}
int tag[N];
void fail() {
puts("0");
exit(0);
}
void dfs(int a) {
int c = 3 - tag[a];
for (auto b : adj[a]) {
if (!tag[b]) {
tag[b] = c;
dfs(b);
} else if (tag[b] != c) {
fail();
}
}
}
class {
int data[N];
void add(int p, int v) {
for (; p <= 2 * n; p += p & -p) data[p] += v;
}
public:
void clear() {
memset(data, 0, sizeof data);
}
void add(int l, int r, int v) {
add(l, v);
add(r + 1, -v);
}
int query(int p) {
int res = 0;
for (; p; p ^= p & -p) res += data[p];
return res;
}
} bit;
void check(int y) {
bit.clear();
for (int i = 1; i <= 2 * n; ++i) {
int x = id[i];
if (tag[x] != y) continue;
if (c[i] > i) {
bit.add(1, i, 1);
} else {
bit.add(1, c[i], -1);
if (bit.query(c[i])) fail();
bit.add(c[i], i, 1);
}
}
}
int main() {
scanf("%d", &n);
for (int i = 1; i <= n; ++i) a[i] = nextInt(), b[i] = nextInt();
for (int i = 1; i <= n; ++i) c[a[i]] = b[i], c[b[i]] = a[i], id[a[i]] = id[b[i]] = i;
for (int i = 1; i <= 2 * n; ++i) {
if (c[i] > i) continue;
query(c[i], id[i]);
update(c[i], id[i]);
}
int cnt = 0;
for (int i = 1; i <= n; ++i) if (!tag[i]) ++cnt, tag[i] = 1, dfs(i);
check(1);
check(2);
int ans = 1;
while (cnt--) ans = 2 * ans % MOD;
printf("%d\n", ans);
return 0;
}
Compilation message
port_facility.cpp: In function 'void dfs(int)':
port_facility.cpp:54:8: warning: 'auto' changes meaning in C++11; please remove it [-Wc++0x-compat]
for (auto b : adj[a]) {
^
port_facility.cpp:54:13: error: 'b' does not name a type
for (auto b : adj[a]) {
^
port_facility.cpp:62:1: error: expected ';' before '}' token
}
^
port_facility.cpp:62:1: error: expected primary-expression before '}' token
port_facility.cpp:62:1: error: expected ';' before '}' token
port_facility.cpp:62:1: error: expected primary-expression before '}' token
port_facility.cpp:62:1: error: expected ')' before '}' token
port_facility.cpp:62:1: error: expected primary-expression before '}' token
port_facility.cpp:53:7: warning: unused variable 'c' [-Wunused-variable]
int c = 3 - tag[a];
^
port_facility.cpp: At global scope:
port_facility.cpp:82:3: warning: anonymous type with no linkage used to declare variable '<anonymous class> bit' with linkage
} bit;
^
port_facility.cpp: In function 'int main()':
port_facility.cpp:100:18: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
scanf("%d", &n);
^
