Tarjan & Strongly Connected Component

版权声明：copy right https://blog.csdn.net/qq_43521140/article/details/90817601

Example:
①luogu P2661
②luogu P2921

Template_code:

#include<bits/stdc++.h>
#define fuck cout << "fuck" << endl;
#define mem(a,b) memset(a,b,sizeof(a))
#define Fast ios::sync_with_stdio(false);
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
const int base = 13331;
const int MX = 1e5 + 7;
const int INF = 0x3f3f3f3f;
const ll LINF = 0x3f3f3f3f3f3f3f3f;
vector<edge> G[MX];
int DFN[MX];
int LOW[MX];
bool ins[MX];
stack<int>s;
int timing;
int color[MX];//the number of SCC that node i belongs to
int colornum[MX];//the number of nodes that belongs to SCC i
int colorcnt;

//present node u
void tarjan(int u){
	timing++;
	DFN[u] = LOW[u] = timing;
	s.push(u);
	ins[u] = true;
	for(int v : G[u]){
		//if its son node hasn't been visted
		if(DFN[v] == 0){
			tarjan(v);
			LOW[u] = min(LOW[u],LOW[v]);
		}
		//node v is not a key node
		else if(ins[v] == true){
			LOW[u] = min(LOW[u],DFN[v]);
		}
	}

	//node u is a key node
	if(DNF[u] == LOW[u]){
		cnt++;
		while(s.top() != u){
			int tmp = s.top();
			s.pop();
			//out of the stack
			ins[tmp] = false;

			//node tmp belongs to SCC colorcnt
			color[tmp] = colorcnt;

			//the number of nodes SCC colorcnt has
			colornum[colorcnt]++;
		}

		//the node u itself
		s.pop();
		color[u] = colorcnt;
		colornum[colorcnt]++;
		ins[u] = false;
	}
}

int main(int argc, char const *argv[]){
#ifdef local
    freopen("Input_File.txt","r",stdin);
    freopen("Output_File.txt","w",stdout);
#endif
	int n,m;
	int x,y;
	for(int i = 1;i <= m;++i){
		cin >> x >> y;
		G[x].push_back(y);
	}
	for(int i = 1;i <= n;++i){
		if(DFN[i] == 0){
			tarjan(i);
		}
	}
    return 0;
}

/*


*/