無向圖的雙聯通分量

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點雙和邊雙的區別我在上一篇文章中已經討論過了，這篇文章講邊雙的求法。

由於是邊雙，就決定了邊雙中一定不含有橋，但是可以含有割頂。

所以我們對邊雙唯一的限制條件就是不經過橋。

如此一來，我們可以分成兩次dfs，第一次求出所有的橋，第二次dfs時遍曆整張圖，只要保證不經過橋就可以了。

#include <cstdio>#include <cstring>#include <algorithm>#include <vector>#include <stack>using namespace std;const int maxn = 105, maxm = maxn * 2;int n, m, tot, dfs_clock, bcc_cnt;int h[maxn], dfn[maxn], low[maxn], iscut[maxn], vis[maxn]; struct edge{    int v, next, isbridge;}a[maxm];vector<int> bcc[maxn];void add(int x, int y){    a[tot].v = y;    a[tot].next = h[x];    h[x] = tot++;}int dfs(int u, int fa){    int lowu = dfn[u] = ++dfs_clock;    int child = 0;    for (int i = h[u]; ~i; i = a[i].next)    {        int v = a[i].v;        if (!dfn[v])        {            child++;            int lowv = dfs(v, u);            lowu = min(lowu, lowv);            if (lowv >= dfn[u])            {                iscut[u] = 1;            }            if (lowv > dfn[u])            {//                printf("%d - %d\n", u, v);                a[i].isbridge = 1;                a[i^1].isbridge = 1;            }        }else if (dfn[v] < dfn[u] && v != fa)        {            lowu = min(lowu, dfn[v]);        }    }    if (fa == 0 && child == 1)    {        iscut[u] = 0;    }    low[u] = lowu;    return lowu;}void dfs2(int u, int fa){    bcc[bcc_cnt].push_back(u);    vis[u] = 1;    for (int i = h[u]; ~i; i = a[i].next)    {        int v = a[i].v;        if (v == fa || a[i].isbridge ||vis[v]) continue;        dfs2(v, u);    } }int main(){    freopen("無向圖雙聯通分量.in","r",stdin);    scanf("%d%d", &n, &m);    memset(h, -1, sizeof h); tot = dfs_clock = 0;    for (int i = 1; i <= m; i++)    {        int x, y;        scanf("%d%d", &x, &y);        add(x, y); add(y, x);    }    dfs(1, 0);    for (int i = 1; i <= n; i++)        if (!vis[i])        {            bcc_cnt++;            bcc[bcc_cnt].clear();            dfs2(i, 0);        }    for (int i = 1; i <= bcc_cnt; i++)    {        for (int j = 0; j < bcc[i].size(); j++)            printf("%d ", bcc[i][j]);        printf("\n");    }    return 0;}

 

無向圖的雙聯通分量