UVA 796 Critical Links

输出桥。

#include<cstdio>
#include<cstring>
#include<cmath>
#include<vector>
#include<algorithm>
using namespace std;

const int maxn = 10000 + 10;
const int Maxn = 2 * 100000 + 10; 
int low[maxn];
int dfn[maxn];
int U[maxn], V[maxn];

struct Edge
{
    int from, to, id, ans;
} edge[Maxn];
vector<int>G[maxn];
int N, M;
int tmpdfn;
int tot;
int Start, End;

struct ANSS
{
    int first, second;
}ANS[Maxn];

void init()
{
    for (int i = 0; i<maxn; i++) G[i].clear();
    memset(low, 0, sizeof(low));
    memset(dfn, 0, sizeof(dfn));
    low[1] = dfn[1] = 1;
    tmpdfn = 0;
    tot = 0;
}

void AddEdge(int u, int v)
{
    edge[tot].from = u;
    edge[tot].to = v;
    edge[tot].id = tot;
    edge[tot].ans = 0;
    G[u].push_back(tot);
    tot++;
    
    edge[tot].from = v;
    edge[tot].to = u;
    edge[tot].id = tot;
    edge[tot].ans = 0;
    G[v].push_back(tot);
    tot++;
    
}

int Tarjan(int u, int id)
{
    tmpdfn++;
    int lowu = dfn[u] = tmpdfn;
    for (int i = 0; i<G[u].size(); i++)
    {
        int B = G[u][i];
        if (!dfn[edge[B].to])
        {
            int lowv = Tarjan(edge[B].to, edge[B].id);
            lowu = min(lowu, lowv);
            if (lowv >= dfn[u])
            {
                if (lowv>dfn[u])
                    edge[B].ans = 1;
            }
        }
        else if (dfn[edge[B].to])
        {
            if (edge[B].id / 2 == id / 2) continue;
            lowu = min(lowu, dfn[edge[B].to]);
        }
    }

    low[u] = lowu;
    return lowu;
}

bool cmp(const ANSS&a, const ANSS&b)
{
    if (a.first == b.first) return a.second < b.second;
    return a.first < b.first;
}

void Display_Cutting_edge()
{
    int AA = 0;
    for (int i = 0; i < 2 * M; i++)
    {
        if (edge[i].ans)
        {
            if (edge[i].from < edge[i].to)
            {
                ANS[AA].first = edge[i].from;
                ANS[AA].second = edge[i].to;
            }
            else
            {
                ANS[AA].first = edge[i].to;
                ANS[AA].second = edge[i].from;
            }
            AA++;
        }
    }
    printf("%d critical links\n", AA);
    sort(ANS, ANS + AA, cmp);
    for (int i = 0; i < AA; i++)
        printf("%d - %d\n", ANS[i].first-1, ANS[i].second-1);
    printf("\n");
}


int main()
{
    while (~scanf("%d", &N))
    {
        init();
        M = 0;
        for (int i = 1; i <= N; i++)
        {
            int from,TTT;
            scanf("%d (%d)", &from, &TTT);
            while (TTT--)
            {
                int too;
                scanf("%d", &too);
                if (from >= too) continue;
                U[M] = from + 1; V[M] = too + 1;
                AddEdge(U[M], V[M]);
                M++;
            }
        }
        Start = 1; End = N;
        Tarjan(1, -1);
        for (int i = 2; i <= N; i++) if (!dfn[i]) Tarjan(i, -1);
        Display_Cutting_edge();
    }
    return 0;
}