[UVA796]Critical Links(割边, 桥)

Posted 2020-07-09

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。

  1 /*
  2 ━━━━━┒ギリギリ♂ eye！
  3 ┓┏┓┏┓┃キリキリ♂ mind！
  4 ┛┗┛┗┛┃＼○／
  5 ┓┏┓┏┓┃ /
  6 ┛┗┛┗┛┃ノ)
  7 ┓┏┓┏┓┃
  8 ┛┗┛┗┛┃
  9 ┓┏┓┏┓┃
 10 ┛┗┛┗┛┃
 11 ┓┏┓┏┓┃
 12 ┛┗┛┗┛┃
 13 ┓┏┓┏┓┃
 14 ┃┃┃┃┃┃
 15 ┻┻┻┻┻┻
 16 */
 17 #include <algorithm>
 18 #include <iostream>
 19 #include <iomanip>
 20 #include <cstring>
 21 #include <climits>
 22 #include <complex>
 23 #include <fstream>
 24 #include <cassert>
 25 #include <cstdio>
 26 #include <bitset>
 27 #include <vector>
 28 #include <deque>
 29 #include <queue>
 30 #include <stack>
 31 #include <ctime>
 32 #include <set>
 33 #include <map>
 34 #include <cmath>
 35 
 36 using namespace std;
 37 
 38 #define fr first
 39 #define sc second
 40 #define cl clear
 41 #define BUG puts("here!!!")
 42 #define W(a) while(a--)
 43 #define pb(a) push_back(a)
 44 #define Rint(a) scanf("%d", &a)
 45 #define Rll(a) scanf("%lld", &a)
 46 #define Rs(a) scanf("%s", a)
 47 #define Cin(a) cin >> a
 48 #define FRead() freopen("in", "r", stdin)
 49 #define FWrite() freopen("out", "w", stdout)
 50 #define Rep(i, len) for(int i = 0; i < (len); i++)
 51 #define For(i, a, len) for(int i = (a); i < (len); i++)
 52 #define Cls(a) memset((a), 0, sizeof(a))
 53 #define Clr(a, x) memset((a), (x), sizeof(a))
 54 #define Full(a) memset((a), 0x7f7f, sizeof(a))
 55 #define lp p << 1
 56 #define rp p << 1 | 1
 57 #define pi 3.14159265359
 58 #define RT return
 59 typedef long long LL;
 60 typedef long double LD;
 61 typedef unsigned long long ULL;
 62 typedef pair<int, int> pii;
 63 typedef pair<string, int> psi;
 64 typedef map<string, int> msi;
 65 typedef vector<int> vi;
 66 typedef vector<LL> vl;
 67 typedef vector<vl> vvl;
 68 typedef vector<bool> vb;
 69 
 70 const int maxn = 100010;
 71 typedef struct Bridge {
 72     int u, v;
 73     Bridge() {}
 74     Bridge(int uu, int vv) : u(uu), v(vv) { if(u > v) swap(u, v); }
 75 }Bridge;
 76 
 77 int n;
 78 int dfn[maxn], low[maxn];
 79 vi G[maxn];
 80 vector<Bridge> b;
 81 
 82 void dfs(int u, int d, int p) {
 83     low[u] = dfn[u] = d;
 84     Rep(i, G[u].size()) {
 85         int v = G[u][i];
 86         if(!dfn[v]) {
 87             dfs(v, d+1, u);
 88             low[u] = min(low[u], low[v]);
 89             if(low[v] > dfn[u]) b.push_back(Bridge(u, v));
 90         }
 91         else if(p != v) low[u] = min(low[u], dfn[v]);
 92     }
 93 }
 94 
 95 bool cmp(Bridge x, Bridge y) {
 96     if(x.u == y.u) return x.v < y.v;
 97     return x.u < y.u;
 98 }
 99 
100 int main() {
101     // FRead();
102     int u, v, p;
103     while(~Rint(n)) {
104         if(n == 0) {
105             printf("0 critical links\n\n");
106             continue;
107         }
108         Cls(dfn); Cls(low); b.cl();
109         Rep(i, n+5) G[i].cl();
110         Rep(i, n) {
111             Rint(u);
112             scanf(" (%d) ", &p);
113             W(p) {
114                 Rint(v);
115                 G[u].push_back(v);
116                 G[v].push_back(u);
117             }
118         }
119         Rep(i, n) if(!dfn[i]) dfs(i, 0, i);
120         sort(b.begin(), b.end(), cmp);
121         printf("%d critical links\n", b.size());
122         Rep(i, b.size()) {
123             printf("%d - %d\n", b[i].u, b[i].v);
124         }
125         printf("\n");
126     }
127     RT 0;
128 }