用tarjan缩点
然后用dfn[u] < low[v]缩点并且保存起来
在sort一遍输出
#include<stdio.h>
#include<string.h>
#include<algorithm>
using namespace std;
const int maxn = 10000;
struct Node {
int u;
int v;
int next;
};
struct Edge{
int u;
int v;
};
Edge edge[maxn];
Node node[maxn * 10];
int head[maxn];
int dfn[maxn];
int low[maxn];
int fath[maxn];
bool vis[maxn];
bool maps[maxn][maxn];
int n, tol, cnt;
void init() {
cnt = tol= 0;
memset(dfn, 0, sizeof(dfn));
memset(low, 0, sizeof(low));
memset(maps, 0, sizeof(maps));
memset(fath, 0, sizeof(fath));
memset(head, -1, sizeof(head));
memset(vis, false, sizeof(vis));
}
void addnode(int u, int v) {
node[tol].u = u;
node[tol].v = v;
node[tol].next = head[u];
head[u] = tol++;
}
void dfs(int u, int fa){
fath[u] = fa;
low[u] = dfn[u] = ++cnt;
vis[u] = true;
for(int i=head[u]; i!=-1; i=node[i].next) {
int v = node[i].v;
if(!dfn[v]) {
dfs(v, u);
low[u] = min(low[u], low[v]);
} else if(v != fa) {
low[u] = min(low[u], dfn[v]);
}
}
}
void tarjan() {
for(int u=0; u<n; u++) {
if(!dfn[u]) {
dfs(u, u);
}
}
}
bool cmp(Edge a, Edge b) {
if(a.u == b.u)
return a.v < b.v;
else
return a.u < b.u;
}
void solve() {
tol = 0;
for(int u=0; u<n; u++) {
int v = fath[u];
if(low[u] > dfn[v] && v != u) {
edge[tol].u = u;
edge[tol].v = v;
if(edge[tol].u > edge[tol].v)
swap(edge[tol].u, edge[tol].v);
tol++;
}
}
sort(edge, edge+tol, cmp);
printf("%d critical links\n", tol);
for(int i=0; i<tol; i++) {
printf("%d - %d\n", edge[i].u, edge[i].v);
}
printf("\n");
}
int main() {
while(scanf("%d", &n) != EOF) {
init();
if(n == 0) {
printf("0 critical links\n\n");
continue;
}
for(int i=1; i<=n; i++) {
int u;
int num;
scanf("%d (%d)", &u, &num);
for(int j=1; j<=num; j++) {
int v;
scanf("%d", &v);
maps[u][v] = maps[v][u] = 1;
}
}
for(int i=0; i<n; i++) {
for(int j=i+1; j<n; j++) {
if(maps[i][j]) {
addnode(i, j);
addnode(j, i);
}
}
}
tarjan();
solve();
}
return 0;
}