hdu 3849 By Recognizing These Guys, We Find Social Networks Useful

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判断无向图的割点和桥的模板题，但是这个题要求按照输入的顺序输出边，因此需要把边保存以下，挺麻烦的其实，= =。

#include <map>#include <vector>#include <cstdio>#include <cstring>#include <iostream>#include <algorithm>using namespace std;const int MAX = 10010;typedef pair <int, int> Pii;vector <int> vt[MAX];vector <Pii> ans;map <string, int> mp;map <Pii, int> order;string a, b, name[MAX];int n, m;bool vis[MAX];int cnt_n, cnt_e,dfs_clock;int pre[MAX];void init(){    for(int i=1; i<=n; i++){        vt[i].clear();        pre[i] = 0;        vis[i] = false;    }    mp.clear();    ans.clear();    order.clear();    cnt_e = cnt_n = dfs_clock = 0;}void is_connected(int u){//判断是否连通    vis[u] = true;    for(int i=0; i<vt[u].size(); i++){        int v = vt[u][i];        if(!vis[v]) is_connected(v);    }}bool presolve(){    for(int i=1; i<=n; i++)        if(!vis[i]) return false;    return true;}int dfs(int u, int fa){//tarjan算法求桥    int lowu = pre[u] = ++dfs_clock;    for(int i=0; i<vt[u].size(); i++){        int v = vt[u][i];        if(!pre[v]){            int lowv = dfs(v, u);            lowu = min(lowu, lowv);            if(lowv > pre[u]){                Pii tmp;                tmp.first = u, tmp.second = v;                if(order[tmp] == false)                     tmp.first = v, tmp.second = u;                ans.push_back(tmp);            }        }        else if(pre[v] < pre[u] && v != fa)            lowu = min(lowu, pre[v]);    }    return lowu;}bool cmp(Pii A, Pii B){    return order[A] < order[B];}int main(){    int cas;    scanf("%d",&cas);    while(cas--){        scanf("%d%d",&n,&m);        init();        for(int i=0; i<m; i++){            cin >> a >> b;            if(mp[a] == false){                mp[a] = ++cnt_n;                name[cnt_n] = a;            }            if(mp[b] == false){                mp[b] = ++cnt_n;                name[cnt_n] = b;            }            int u = mp[a], v = mp[b];            vt[u].push_back(v);            vt[v].push_back(u);            Pii tmp;            tmp.first = u, tmp.second = v;            order[tmp] = ++cnt_e;        }        is_connected(1);        if(!presolve()){            puts("0");            continue;        }        dfs(1, -1);        int l = ans.size();        printf("%d\n",l);        sort(ans.begin(), ans.end(), cmp);        for(int i=0; i<l; i++){            cout << name[ans[i].first] << " " << name[ans[i].second] << endl;        }    }    return 0;}

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