版权声明: https://blog.csdn.net/weixin_40959045/article/details/80715847
题意
求割边
tarjan 模板题
#include <map>
#include <set>
#include <queue>
#include <stack>
#include <vector>
#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <iostream>
#include <algorithm>
using namespace std;
#define MAX_V 110
#define MAX_E 10010
#define mem(a) memset((a),0,sizeof(a))
struct edge{
int to;
int next;
};
edge es[MAX_E];
int head[MAX_V],len;
struct BRIDGE{
int u,v;
};
BRIDGE bridge[MAX_E];
int cnt;
int V;
int dfn[MAX_V],low[MAX_V];
int ord;
int stk[MAX_V],top;
int instack[MAX_V];
int bcnt;
void addedge(int from,int to)
{
es[len].to = to;
es[len].next = head[from];
head[from] = len++;
}
bool cmp(BRIDGE& a,BRIDGE& b){
if (a.u == b.u){
return a.v < b.v;
}
return a.u < b.u;
}
void tarjan(int u,int fa){
dfn[u] = low[u] = ++ord;
instack[u] = 1;
stk[top++] = u;
for (int i = head[u];i != -1;i = es[i].next){
int v = es[i].to;
if (v == fa){
continue;
}
if (dfn[v] == -1){
tarjan(v,u);
if (low[u] > low[v]){
low[u] = low[v];
}
if (low[v] > dfn[u]){
bridge[cnt].u = min(u,v);
bridge[cnt++].v = max(u,v);
}
} else if (instack[v]){
if(dfn[v] < low[u]){
low[u] = dfn[v];
}
}
}
if (dfn[u] == low[u]){
bcnt++;
int v;
do {
v = stk[--top];
instack[v] = 0;
} while (v != u);
}
}
void init(){
cnt = top = len = ord = 0;
mem(low);
mem(instack);
mem(stk);
memset(dfn,-1,sizeof dfn);
memset(head,-1,sizeof head);
}
void solve(){
for (int i = 1;i<=V;i++){
if (dfn[i] == -1){
tarjan(i,-1);
}
}
sort(bridge,bridge+cnt,cmp);
printf("%d critical links\n", cnt);
for (int i = 0;i<cnt;i++){
printf("%d - %d\n", bridge[i].u-1, bridge[i].v-1);
}
printf("\n");
}
int main()
{
int u, v;
int num;
while (~scanf("%d", &V))
{
if (V == 0)
{
printf("0 critical links\n\n");
continue;
}
init();
for (int i = 1; i <= V; ++i)
{
scanf("%d", &u);
++u;
getchar();
getchar();
scanf("%d", &num);
getchar();
while (num--)
{
scanf("%d", &v);
++v;
addedge (u, v);
}
}
solve ();
}
return 0;
}