#include <bits/stdc++.h>
#define F first
#define S second
#define PB push_back
#define PF push_front
#define MP make_pair
using namespace std;
typedef long long ll;
typedef long double ld;
typedef pair<int,int> pii;
const int maxn = 3e4 + 10;
const int block = 320;
int h[maxn], par[maxn], parsqrt[maxn], dp[maxn];
bool cut[maxn];
int lca (int v, int u) {
if (h[v] < h[u])
swap (v, u);
while (h[v] > h[u]) {
if (h[v] - block >= h[u])
v = parsqrt[v];
else
v = par[v];
}
if (v == u)
return v;
while (v != u) {
if (parsqrt[v] != parsqrt[u]) {
v = parsqrt[v];
u = parsqrt[u];
}
else {
v = par[v];
u = par[u];
}
}
return v;
}
vector <int> g[maxn];
void dfs2 (int v, int p) {
dp[v] = h[v];
for (auto w : g[v]) {
if (w != p) {
h[w] = h[v] + 1;
dfs2 (w, v);
}
}
}
void dfs1 (int v, int p) {
par[v] = p;
parsqrt[v] = p;
for (int i = 1; i < block; i++)
parsqrt[v] = par[parsqrt[v]];
for (auto u : g[v]) {
if (u != p) {
dfs1 (u, v);
if (h[v] > h[u])
cut[u] = cut[v];
}
}
}
void dfs (int v, int p = -1) {
for (auto w : g[v]) {
if (w != p) {
dfs (w, v);
dp[v] = min (dp[v], dp[w]);
}
}
cut[v] &= (h[v] <= dp[v]);
}
int dpar[maxn];
int get_par (int v) {
if (dpar[v] < 0)
return v;
return dpar[v] = get_par (dpar[v]);
}
int n;
void merge (int v, int u) {
int vpar = get_par (v), upar = get_par (u);
dfs (vpar);
dfs1 (v, u);
cut[v] = 1;
h[v] = h[u] + 1;
dfs2 (v, u);
dpar[upar] += dpar[vpar];
dpar[vpar] = upar;
g[u].PB (v);
g[v].PB (u);
}
int main() {
memset (par, -1, sizeof par);
memset (dpar, -1, sizeof dpar);
int m;
cin >> n >> m;
while (m --) {
int v, u;
cin >> v >> u;
int vpar = get_par(v), upar = get_par(u);
if (vpar != upar) {
if (dpar[vpar] < dpar[upar])
swap (v, u);
merge (v, u);
}
else {
int w = lca (v, u);
dp[v] = min (dp[v], h[w]);
dp[u] = min (dp[u], h[w]);
}
}
for (int i = 1; i <= n; i++)
if (dpar[i] < 0)
dfs (v);
for (int i = 1; i <= n; i++)
if (cut[i])
cout << i << " " << par[i] << endl;
}
Compilation message
pipes.cpp: In function 'int main()':
pipes.cpp:122:9: error: 'v' was not declared in this scope
dfs (v);
^
