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>
#pragma GCC optimize("O2", "fast-math")
using namespace std;
typedef long long int ll;
typedef pair<int, int> pii;
#define SZ(x) (int) x.size()
#define F first
#define S second
const int N = 1e5 + 10, MOD = 1e9 + 7;
int dp[N], M[N], dp2[N], up[N], P[N], H[N], rt[N], fr[N], to[N], n, m; vector<int> vec[N], adj[N];
int pd[N];
void add(int &x, int y) {
x += y;
if (x >= MOD) x -= MOD;
if (x < 0) x += MOD;
}
int Find(int v) { return !rt[v] ? v : rt[v] = Find(rt[v]); }
void Union(int u, int v) {
u = Find(u), v = Find(v);
if (u == v) return;
vec[v].push_back(u);
rt[u] = v;
}
void preDFS(int v, int p = -1) {
M[v] = 1; P[v] = p;
for (int id : adj[v]) {
int u = fr[id] ^ to[id] ^ v;
if (!M[u]) {
H[u] = H[v] + 1; preDFS(u, v);
} else if (u != p && H[u] < H[v]) {
int w = v;
while (w != u)
Union(P[w], w), w = P[w];
}
}
}
void DFS(int v, int p = -1) {
vector<int> tmp;
for (int &u : vec[v])
for (int &w : adj[u])
if (w != p)
DFS(w, v);
else up[v] = u;
}
inline int calc_dp2(vector<int> &A) {
int ret = 0, S = 0;
for (int i = 0; i < SZ(A); i++) {
S = A[i] * 1ll * (S + 1) % MOD;
add(ret, S);
}
return ret;
}
inline int calc_dp1(vector<int> &A) {
int ret = calc_dp2(A), S = 1;
fill(pd, pd + SZ(A) + 1, 0);
for (int i = 0; i < SZ(A); i++) {
S = 1ll * S * A[i] % MOD;
pd[i] = S;
if (i > 0) add(pd[i], pd[i - 1]);
}
S = 1;
for (int i = SZ(A) - 1; i > 1; i--) {
S = 1ll * S * A[i] % MOD;
add(ret, 1ll * S * pd[i - 2] % MOD);
}
return ret;
}
void dpDFS(int v, int p = -1) {
vector<int> A;
if (~p) {
vector<int> tmp;
while (vec[v].back() != up[v])
tmp.push_back(vec[v].back()), vec[v].pop_back();
vec[v].swap(tmp);
for (int &x : tmp)
vec[v].push_back(x);
}
for (int &u : vec[v]) {
A.push_back(1);
for (int &w : adj[u])
if (w != p) dpDFS(w, v), A.back() = A.back() * 1ll * (dp2[w] + 1) % MOD;
}
dp[v] = calc_dp1(A);
if (SZ(vec[v]) > 1) {
int S = 1;
for (int &x : A)
S = 1ll * S * x % MOD;
add(dp[v], -S);
}
if (~p) {
A.pop_back();
add(dp2[v], dp[v] - calc_dp2(A));
}
}
int main() {
scanf("%d%d", &n, &m);
for (int i = 1; i <= n; i++)
vec[i] = {i};
for (int i = 1; i <= m; i++) {
int u, v; scanf("%d%d", &u, &v);
adj[fr[i] = u].push_back(i);
adj[to[i] = v].push_back(i);
}
preDFS(1);
for (int i = 1; i <= n; i++)
Find(i);
for (int i = 1; i <= n; i++)
if (!rt[i]) rt[i] = i;
for (int i = 1; i <= n; i++) {
vector<int> tm;
for (int id : adj[i]) {
int u = fr[id] ^ to[id] ^ i;
if (rt[i] != rt[u]) tm.push_back(rt[u]);
}
adj[i].swap(tm);
}
DFS(rt[1]);
dpDFS(rt[1]);
int ret = 0;
for (int i = 1; i <= n; i++)
if (rt[i] == i) add(ret, dp[i]);
printf("%d\n", ret);
return 0;
}
Compilation message (stderr)
Main.cpp: In function 'int main()':
Main.cpp:108:10: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
108 | scanf("%d%d", &n, &m);
| ~~~~~^~~~~~~~~~~~~~~~
Main.cpp:112:24: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
112 | int u, v; scanf("%d%d", &u, &v);
| ~~~~~^~~~~~~~~~~~~~~~
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