Tarjan directed algorithm for connected component and condensing point Tuqiang

 

// Tarjan algorithm for communicating the condensing point and the component Tuqiang 
#include <the iostream> 
#include <cstdio> 
#include <CString> 
#include <algorithm> 
#include <Vector> 
#include <Queue>
 the using  namespace STD;
 const  int = N 100010 , M = 1000010 ;
 //
 int Ver [M], the Next [M], head [N], DFN [N], Low [N];
 int Stack [N], INS [N], C [N ]; 

int VC [m], NC [m], HC [N], TC;
 // strongly connected components 
Vector < int > SCC [N]; 

int n-, m, TOT, NUM, Top, CNT; 

voidthe Add ( int X, int Y) { 
    Ver [ ++ TOT] = Y, the Next [TOT] = head [X], head [X] = TOT; 
} 
// after condensing point construction of FIG 
void add_c ( int X, int Y) { 
    VC [ ++ TC] = Y, NC [TC] = HC [X], HC [X] = TC; 
} 

void Tarjan ( int X) { 
    DFN [X] = Low [X] ++ = NUM ; 
    Stack [ ++ Top] x =, INS [x] = . 1 ; // tag point x 
    for ( int I = head [x]; I; I = the Next [I])
         // not passed 
        if(! DFN [Ver [I]]) { 
            Tarjan (Ver [I]); 
            // recursive update 
            Low [X] = min (Low [X], Low [Ver [I]]); 
        } 
        the else  IF (INS [ Ver [I]])
             // updated directly 
            Low [X] = min (Low [X], DFN [Ver [I]]);
     IF (DFN [X] == Low [X]) {
         // a strongly connected 
        ++ CNT; int Y;
         do { 
            Y = Stack [top--], INS [Y] = 0 ;
             // belongs to which strongly connected 
            C [Y] = CNT, SCC [CNT] .push_back (Y); 
        } the while (x != y);
    }
}

int main() {
    cin >> n >> m;
    for (int i = 1; i <= m; i++) {
        int x, y;
        scanf("%d%d", &x, &y);
        add(x, y);
    }
    for (int i = 1; i <= n; i++)
        if (!dfn[i]) tarjan(i);
    for (int x = 1; x <= n; x++)
        for (int i = head[x]; i; i = Next[i]) {
            int y = ver[i];
            if (c[x] == c[y]) continue;
            add_c(c[x], c[y]);
        }
}