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65 lines
1.6 KiB
65 lines
1.6 KiB
#include <bits/stdc++.h>
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using namespace std;
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const int N = 5010, M = 20010;
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typedef pair<int, int> PII;
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int n, m;
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int h[N], e[M], ne[M], idx;
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int dfn[N], low[N], timestamp;
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int stk[N], top;
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int id[N], dcc_cnt;
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bool is_bridge[M];
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int d[N];
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vector<PII> res;
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//排序函数
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bool cmp(const PII &a, const PII &b) {
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if (a.first == b.first) return a.second < b.second;
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return a.first < b.first;
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}
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void add(int a, int b) {
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e[idx] = b, ne[idx] = h[a], h[a] = idx++;
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}
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void tarjan(int u, int from) {
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dfn[u] = low[u] = ++timestamp;
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stk[++top] = u;
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for (int i = h[u]; ~i; i = ne[i]) {
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int j = e[i];
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if (!dfn[j]) {
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tarjan(j, i);
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low[u] = min(low[u], low[j]);
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if (dfn[u] < low[j]) {
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res.push_back({min(u, j), max(u, j)});
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is_bridge[i] = is_bridge[i ^ 1] = true;
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}
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} else if (i != (from ^ 1))
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low[u] = min(low[u], dfn[j]);
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}
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if (dfn[u] == low[u]) {
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++dcc_cnt;
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int y;
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do {
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y = stk[top--];
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id[y] = dcc_cnt;
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} while (y != u);
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}
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}
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int main() {
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cin >> n >> m;
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memset(h, -1, sizeof h);
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for (int i = 0; i < m; i++) {
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int a, b;
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cin >> a >> b;
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add(a, b), add(b, a);
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}
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for (int i = 1; i <= n; i++)
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if (!dfn[i]) tarjan(i, -1);
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sort(res.begin(), res.end(), cmp);
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for (int i = 0; i < res.size(); i++)
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cout << res[i].first << " " << res[i].second << endl;
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return 0;
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}
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