Problem Link

Code:

#include <bits/stdc++.h>
using namespace std;

const int N = 30001;
int low[N], dfn[N], dfnTot;
bool isBridge[N];
vector<int> gv[N];
int bridgeCnt;
int father[N];
map<pair<int, int>, bool> vis; 

void tarjan(int u, int fa) {
	father[u] = fa;
	low[u] = dfn[u] = ++dfnTot;
	for (int v: gv[u]) {
		if (!dfn[v]) {
			tarjan(v, u);
			low[u] = min(low[u], low[v]);
			if (low[v] > dfn[u])
				isBridge[v] = true, ++bridgeCnt;
		} else if (dfn[v] < dfn[u] && v != fa)
			low[u] = min(low[u], dfn[v]);
	}
}

int main() {
	int n, m;
	while (cin >> n >> m && (n || m)) {
		memset(low, 0, sizeof low);
		memset(dfn, 0, sizeof dfn);
		memset(isBridge, 0, sizeof isBridge);
		memset(father, 0, sizeof father);
		vis.clear();
		for (int i = 1; i <= n; i++)
			gv[i].clear();
		dfnTot = bridgeCnt = 0;
		for (int i = 1; i <= m; i++) {
			int u, v;
			cin >> u >> v;
			if (vis[{u, v}] || vis[{v, u}])
				continue;
			vis[{u, v}] = 1;
			vis[{v, u}] = 1;
			gv[u].push_back(v);
			gv[v].push_back(u); 
		}
		for (int i = 1; i <= n; i++)
			if (!dfn[i]) 
				tarjan(i, -1);
//		for (int i = 1; i <= n; i++)
//			if (isBridge[i])
//				cout << father[i] << " <--> " << i << endl;
		cout << bridgeCnt << endl;
	}
	return 0;
}

WA $8$ 次了