[UVA796]Critical Links(割边, 桥)

题目链接：https://uva.onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&page=show_problem&problem=737

求桥的数量，也就是割边的数量。输入有点小坑，左右括号外必须得有个空格才行，起初以为是转义的问题。

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 */
 #include <algorithm>
 #include <iostream>
 #include <iomanip>
 #include <cstring>
 #include <climits>
 #include <complex>
 #include <fstream>
 #include <cassert>
 #include <cstdio>
 #include <bitset>
 #include <vector>
 #include <deque>
 #include <queue>
 #include <stack>
 #include <ctime>
 #include <set>
 #include <map>
 #include <cmath>

 using namespace std;

 #define fr first
 #define sc second
 #define cl clear
 #define BUG puts("here!!!")
 #define W(a) while(a--)
 #define pb(a) push_back(a)
 #define Rint(a) scanf("%d", &a)
 #define Rll(a) scanf("%lld", &a)
 #define Rs(a) scanf("%s", a)
 #define Cin(a) cin >> a
 #define FRead() freopen("in", "r", stdin)
 #define FWrite() freopen("out", "w", stdout)
 #define Rep(i, len) for(int i = 0; i < (len); i++)
 #define For(i, a, len) for(int i = (a); i < (len); i++)
 #define Cls(a) memset((a), 0, sizeof(a))
 #define Clr(a, x) memset((a), (x), sizeof(a))
 #define Full(a) memset((a), 0x7f7f, sizeof(a))
 #define lp p << 1
 #define rp p << 1 | 1
 #define pi 3.14159265359
 #define RT return
 typedef long long LL;
 typedef long double LD;
 typedef unsigned long long ULL;
 typedef pair<int, int> pii;
 typedef pair<string, int> psi;
 typedef map<string, int> msi;
 typedef vector<int> vi;
 typedef vector<LL> vl;
 typedef vector<vl> vvl;
 typedef vector<bool> vb;

 const int maxn = ;
 typedef struct Bridge {
     int u, v;
     Bridge() {}
     Bridge(int uu, int vv) : u(uu), v(vv) { if(u > v) swap(u, v); }
 }Bridge;

 int n;
 int dfn[maxn], low[maxn];
 vi G[maxn];
 vector<Bridge> b;

 void dfs(int u, int d, int p) {
     low[u] = dfn[u] = d;
     Rep(i, G[u].size()) {
         int v = G[u][i];
         if(!dfn[v]) {
             dfs(v, d+, u);
             low[u] = min(low[u], low[v]);
             if(low[v] > dfn[u]) b.push_back(Bridge(u, v));
         }
         else if(p != v) low[u] = min(low[u], dfn[v]);
     }
 }

 bool cmp(Bridge x, Bridge y) {
     if(x.u == y.u) return x.v < y.v;
     return x.u < y.u;
 }

 int main() {
     // FRead();
     int u, v, p;
     while(~Rint(n)) {
         if(n == ) {
             printf("0 critical links\n\n");
             continue;
         }
         Cls(dfn); Cls(low); b.cl();
         Rep(i, n+) G[i].cl();
         Rep(i, n) {
             Rint(u);
             scanf(" (%d) ", &p);
             W(p) {
                 Rint(v);
                 G[u].push_back(v);
                 G[v].push_back(u);
             }
         }
         Rep(i, n) if(!dfn[i]) dfs(i, , i);
         sort(b.begin(), b.end(), cmp);
         printf("%d critical links\n", b.size());
         Rep(i, b.size()) {
             printf("%d - %d\n", b[i].u, b[i].v);
         }
         printf("\n");
     }
     RT ;
 }