无向图的双连通分量

点双连通分量模板(Tarjan算法)

#include<bits/stdc++.h>
using namespace std;
#define M(a, b) memset(a, b, sizeof(a))
#define INF 0x3f3f3f3f
const int N = 1000 + 5;
int pre[N], bccno[N], iscut[N], dfs_clock, bcc_cnt;
vector<int> G[N], bcc[N]; 
struct Edge {
    int u, v;
};
stack<Edge> S;

int dfs(int u, int fa) {
    int lowu = pre[u] = ++dfs_clock;
    int child = 0;
    for (int i = 0; i < G[u].size(); ++i) {
        int v = G[u][i];
        if (v == fa) continue;
        Edge now = (Edge){u, v};
        if (!pre[v]) {
            S.push(now);
            ++child;
            int lowv = dfs(v, u);
            lowu = min(lowu, lowv);
            if (lowv >= pre[u]) {
                iscut[v] = true;
                ++bcc_cnt; bcc[bcc_cnt].clear();
                while (1) {
                    Edge e = S.top(); S.pop();
                    if (bccno[e.u] != bcc_cnt) {bcc[bcc_cnt].push_back(e.u); bccno[e.u] = bcc_cnt;}
                    if (bccno[e.v] != bcc_cnt) {bcc[bcc_cnt].push_back(e.v); bccno[e.v] = bcc_cnt;}
                    if (e.u == u && e.v == v) break;
                }
            }
        }
        else if (pre[v] < pre[u]) {
            S.push(now);
            lowu = min(lowu, pre[v]);
        }
    }
    if (fa < 0 && child == 1) iscut[u] = 0;
    return lowu;
}

void find_bcc(int n) {
    M(pre, 0); M(iscut, 0); M(bccno, 0);
    for (int i = 0; i < n; ++i)
        if (!pre[i]) dfs(i, -1);
}

int main() {
    int n, m, u, v;
    cin >> n >> m;
    for (int i = 0; i < m; ++i) {
        cin >> u >> v;
        u--; v--;
        G[u].push_back(v);
        G[v].push_back(u);
    }
    find_bcc(n);
    for (int i = 1; i <= bcc_cnt; ++i) {
        for (int j = 0; j < bcc[i].size(); ++j)
            cout << bcc[i][j]+1 << " ";
        cout << endl;
    }

    return 0;
}

边双连通分量模板(Tarjan算法）

#include<bits/stdc++.h>
using namespace std;
#define M(a, b) memset(a, b, sizeof(a))
#define INF 0x3f3f3f3f
const int N = 1000 + 5;
int pre[N], bccno[N], dfs_clock, bcc_cnt;
vector<int> G[N];

stack<int> S;
int dfs(int u, int fa) {
    int lowu = pre[u] = ++dfs_clock;
    S.push(u);
    for (int i = 0; i < G[u].size(); ++i) {
        int v = G[u][i];
        if (v == fa) continue;
        if (!pre[v]) {
            int lowv = dfs(v, u);
            lowu = min(lowu, lowv);
        }
        else lowu = min(lowu, pre[v]);
    }
    if (lowu == pre[u]) {
        ++bcc_cnt;
        while (1) {
            int k = S.top(); S.pop();
            bccno[k] = bcc_cnt;
            if (k == u) break; 
        }
    }
    return lowu;
}

void find_bcc(int n) {
    M(pre, 0); M(bccno, 0); dfs_clock = bcc_cnt = 0;
    for (int i = 0; i < n; ++i)
        if (!pre[i]) dfs(i, -1);
}


int main() {
    int n, m, u, v;
    cin >> n >> m;
    for (int i = 0; i < m; ++i) {
        cin >> u >> v;
        u--; v--;
        G[u].push_back(v);
        G[v].push_back(u);
    }
    find_bcc(n);

    return 0;
}