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OI-codes/BZOJ/1718/1718.cpp

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#include <iostream>
#include <stack>
using std::cin;
using std::cout;
using std::endl;
const int N = 5005,
M = 10005;
int f, r, ans;
// Graph
int idx, head[N], edge[M], next[M];
void add(int u, int v) {
next[idx] = head[u];
edge[idx] = v;
head[u] = idx++;
}
// Tarjan
int cnt, dfn[N], low[N];
int dcc_cnt, id[N];
std::stack<int> st;
int deg[N];
bool bridge[N];
void tarjan(int u, int in_edge) {
dfn[u] = low[u] = ++cnt;
st.push(u);
for (int i = head[u]; ~i; i = next[i]) {
int v = edge[i];
if (!dfn[v]) {
tarjan(v, i);
low[u] = std::min(low[u], low[v]);
if (dfn[u] < low[v]) {
bridge[i] = bridge[i ^ 1] = true;
}
} else if (i != (in_edge ^ 1)) {
low[u] = std::min(low[u], dfn[v]);
}
}
if (low[u] == dfn[u]) {
dcc_cnt++;
int v;
do {
v = st.top();
st.pop();
id[v] = dcc_cnt;
} while (v != u);
}
}
int main() {
std::fill(head, head + N, -1);
cin >> f >> r;
for (int i = 1; i <= r; i++) {
int u, v;
cin >> u >> v;
add(u, v);
add(v, u);
}
tarjan(1, -1);
for (int i = 0; i < idx; i++) {
if (bridge[i]) {
deg[id[edge[i]]]++;
}
}
for (int i = 1; i <= dcc_cnt; i++) {
if (deg[i] == 1) ans++;
}
cout << (ans + 1 >> 1) << endl;
return 0;
}