Strongly Connected Components

#include <memory.h>

struct edge {
    int e, nxt;
};

int V, E;
edge e[MAXE], er[MAXE];
int sp[MAXV], spr[MAXV];
int group_cnt, group_num[MAXV];
bool v[MAXV];
int stk[MAXV];

void fill_forward(int x){
    int i;
    v[x]=true;
    for(i = sp[x]; i; i = e[i].nxt) 
        if(!v[e[i].e]) fill_forward(e[i].e);
    stk[++stk[0]] = x;
}

void fill_backward(int x){
    int i;
    v[x]=false;
    group_num[x]=group_cnt;
    for(i=spr[x];i;i=er[i].nxt) 
        if(v[er[i].e]) fill_backward(er[i].e);
}

void add_edge(int v1, int v2) {
    e[++E].e = v2; 
    e[E].nxt = sp [v1]; 
    sp[v1] = E;
    er[E].e = v1; 
    er[E].nxt = spr[v2]; 
    spr[v2] = E;
}

void SCC() {
    int i;
    stk[0] = 0;
    memset(v, false, sizeof(v));
    for(i = 1;i <= V;i++) 
        if(!v[i]) fill_forward(i);
    group_cnt = 0;
    for(i = stk[0]; i>= 1; i--) 
        if(v[stk[i]]) {
            group_cnt++; 
            fill_backward(stk[i]);
        }
}