HDU [P3849]

tarjan 求 无向图的割边 (桥)

#include <iostream>
#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <algorithm>
#include <string>
#include <map>
using namespace std;
const int MAXN = 10005, MAXM = 200005;
int head[MAXN], nume, n, m, dfn[MAXN], low[MAXN], ind, cnt, T, tot;
map <string, int> Hash;
string s[MAXN];
bool f[MAXM];
struct edge{
int to, nxt;
}e[MAXM];
void adde(int from, int to) {
e[++nume].to = to;
}
void tarjan(int u, int id) {
dfn[u] = low[u] = ++ind;
for(int i = head[u]; i; i = e[i].nxt) {
int v = e[i].to;
if(!dfn[v]) {
tarjan(v, i);
low[u] = min(low[u], low[v]);
if(low[v] > dfn[u]) {
f[i] = f[((i - 1) ^ 1) + 1] = 1;
}
}else if(i != ((id - 1) ^ 1) + 1) low[u] = min(low[u], dfn[v]);
}
}
int main() {
cin >> T;
while(T--) {
cin >> n >> m;
memset(f, 0, sizeof(f));
nume = ind = tot = cnt = 0;
memset(dfn, 0, sizeof(dfn));
memset(low, 0, sizeof(low));
Hash.clear();
for(int i = 1; i <= m; i++) {
string s1, s2;
cin >> s1 >> s2;
int u = Hash[s1];
if(!u) u = ++tot, s[u] = s1;
Hash[s1] = u;
int v = Hash[s2];
if(!v) v = ++tot; s[v] = s2;
Hash[s2] = v;
}
tarjan(1, 0);
int fff = 1;
for(int i = 1; i <= tot; i++) if(!dfn[i]) {fff = 0;break;}
if(!fff) {
printf("0\n"); continue;
}
for(int i = 1; i <= nume; i++) if(f[i]) cnt++;
cnt /= 2;
cout << cnt << endl;
for(int i = 1; i < nume; i += 2) {
if(f[i]) cout << s[e[((i - 1) ^ 1) + 1].to] << " " << s[e[i].to] << endl;
}
}
}
posted @ 2018-04-02 15:01  Mr_Wolfram  阅读(...)  评论(...编辑  收藏