AC代码：

#include <bits/stdc++.h>
using namespace std;
const int maxn = 1e5 + 5;
int n, m, dfn[maxn], low[maxn], idx;
struct Edge {
	int v, id;
};
vector<Edge> g[maxn];
bool cut[maxn*2];

void tarjan(int u, int pe) {
	dfn[u] = low[u] = ++idx;
	for (auto e : g[u]) {
		int v = e.v, id = e.id;
		if (id == pe) continue;
		if (!dfn[v]) {
			tarjan(v, id);
			low[u] = min(low[u], low[v]);
		}
		else low[u] = min(low[u], dfn[v]);
	}
	if (low[u] == dfn[u])
		cut[pe] = true;
}

int main() {
	scanf("%d%d", &n, &m);
	for (int i = 1; i <= m; i++) {
		int u, v;
		scanf("%d%d", &u, &v);
		g[u].push_back({v, i});
		g[v].push_back({u, i});
	}
	for (int i = 1; i <= n; i++)
		if (!dfn[i])
			tarjan(i, 0);
	int cnt = 0;
	for (int i = 1; i <= m; i++)
		cnt += cut[i];
	printf("%d\n", cnt);
	for (int i = 1; i <= m; i++)
		if (cut[i])
			printf("%d ", i);
	return 0;
}