邊雙聯通分量

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#include <vector>#include <cstdio>#include <cstring>#include <iostream>#include <algorithm>#define maxn 1005#define maxm 1000005using namespace std;struct Edge{    int u,v;    Edge(int u=0,int v=0):u(u),v(v){}}e[maxm];int n,m,stamp,dfn[maxn],low[maxn],bccno[maxn],bcc_cnt;vector<int> vec[maxn];bool isbridge[maxm];void tarjan(int index,int fa){    int tmp;    dfn[index]=low[index]=++stamp;    for(int i=0;i<vec[index].size();i++)    {        tmp=e[vec[index][i]].v;        if(!dfn[tmp])        {            tarjan(tmp,index);            low[index]=min(low[index],low[tmp]);            if(low[tmp]>dfn[index])                isbridge[vec[index][i]]=isbridge[vec[index][i]^1]=1;        }        else if(dfn[tmp]<dfn[index] && tmp!=fa)        {            low[index]=min(low[index], dfn[tmp]);        }    }}void dfs(int index){    dfn[index]=1;    bccno[index]=bcc_cnt;    for(int i=0;i<vec[index].size();i++)    {        int tmp=vec[index][i];        if(isbridge[tmp])            continue;        if(!dfn[e[tmp].v])        {            dfs(e[tmp].v);        }    }}void find_ebcc(){    bcc_cnt=stamp=0;    memset(dfn,0,sizeof(dfn));    memset(low,0,sizeof(low));    memset(bccno,0,sizeof(bccno));    memset(isbridge,0,sizeof(isbridge));    for(int i=1;i<=n;i++)        if(!dfn[i])            tarjan(i, -1);    memset(dfn,0,sizeof(dfn));    for(int i=1;i<=n;i++)    {        if(!dfn[i])        {            bcc_cnt++;            dfs(i);        }    }               }int main(){    while(~scanf("%d %d",&n,&m))    {        memset(vec,0,sizeof(vec));        int x,y;        for(int i=0;i<m;i++)        {            scanf("%d %d",&x,&y);            e[i*2]=Edge(x,y);            vec[x].push_back(2*i);            e[i*2+1]=Edge(y,x);            vec[y].push_back(2*i+1);        }        find_ebcc();        if(bcc_cnt==1)            printf("0\n");        else        {            memset(dfn,0,sizeof(dfn));            for(int i=0;i<m*2;i+=2)            {                x=e[i].u, y=e[i].v;                if(bccno[x]!=bccno[y])                {                    dfn[bccno[x]]++;                    dfn[bccno[y]]++;                }            }            int a=0,b=0;            for(int i=1;i<=bcc_cnt;i++)            {                if(dfn[i]==0)                    a++;                if(dfn[i]==1)                    b++;            }            printf("%d\n",a+(b+1)/2);                   }    }    return 0;}

邊雙聯通分量