UVa247: Calling Circles 题解-优快云博客

本文链接：https://blog.youkuaiyun.com/IcePrincess_1968/article/details/76682336

本文介绍了一种使用Tarjan算法寻找强连通分量的方法，并通过一个具体的C++实现示例来展示其工作原理。该算法在图论中有着广泛的应用，尤其是在处理复杂网络结构时能够有效地找出所有强连通分量。

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有很多算法是用floyd求传递闭包

但感觉裸的tarjan效率更高

#include <cstdio>
#include <iostream>
#include <cstring>
#include <string>
#include <cmath>
#include <algorithm>
#include <cstdlib>
#include <utility>
#include <map>
#include <stack>
#include <set>
#include <vector>
#include <queue>
#include <deque>
#include <sstream>
#define x first
#define y second
#define mp make_pair
#define pb push_back
#define LL long long
#define Pair pair<int,int>
#define LOWBIT(x) x & (-x)
using namespace std;

const int MOD=1e9+7;
const int INF=0x7ffffff;
const int magic=348;

struct node
{
	int indexx;
	int lowlink;
}v[148];

vector<int> edge[148];

int indexx;
map<Pair,bool> judge;
map<string,int> m;
map<int,string> name;
int n,e,tot;
stack<int> sta;
bool visited[148]; 

void tarjan(int cur)
{
	visited[cur]=true;
	sta.push(cur);
	v[cur].indexx=v[cur].lowlink=++indexx;
	int i,x;
	for (i=0;i<edge[cur].size();i++)
	{
		x=edge[cur][i];
		if (v[x].indexx==0)
		{
			tarjan(x);
			v[cur].lowlink=min(v[cur].lowlink,v[x].lowlink);
		}
		else
		{
			if (visited[x]) v[cur].lowlink=min(v[cur].lowlink,v[x].indexx);
		}
	}
	if (v[cur].indexx==v[cur].lowlink)
	{
		do
		{
			x=sta.top();sta.pop();
			cout<<name[x];
			visited[x]=false;
			if (x!=cur) printf(", ");
		}
		while (cur!=x);
		printf("\n");
	}
}

int main ()
{
	int i,ca=0;string s1,s2;
	while (scanf("%d%d",&n,&e) && (n || e))
	{
		//if (ca) printf("\n");
		m.clear();name.clear();tot=0;indexx=0;//judge.clear();
		for (i=1;i<=n;i++) edge[i].clear();
		for (i=1;i<=n;i++) v[i].indexx=v[i].lowlink=0;
		for (i=1;i<=n;i++) visited[i]=false;
		for (i=1;i<=e;i++)
		{
			cin>>s1>>s2;
			if (!m[s1])
			{
				m[s1]=++tot;
				name[tot]=s1;
			}
			if (!m[s2])
			{
				m[s2]=++tot;
				name[tot]=s2;
			}
			//if (judge[mp(m[s1],m[s2])]) continue;
			edge[m[s1]].pb(m[s2]);
			//judge[mp(m[s1],m[s2])]=true;
		}
		printf("Calling circles for data set %d:\n",++ca);
		for (i=1;i<=n;i++)
			if (!v[i].indexx) tarjan(i);
	}
	return 0;
}