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scc.cpp
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scc.cpp
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/* scc */
const int MAXN = 1e3+5;
vector<int> adj[MAXN], adjReverse[MAXN];
int components[MAXN]; // components[i] indicates to which component vertex i belong to.
int n, m, numberOfComponents, in_degree[MAXN];
bool vis[MAXN];
stack<int> stk;
void init(){
for(int i = 1;i <= n; i++){
vis[i] = false;
adj[i].clear();
adjReverse[i].clear();
in_degree[i] = 0;
components[i] = 0;
numberOfComponents = 0;
}
}
void dfs0(int u){
vis[u] = 1;
for(auto v : adj[u]){
if(!vis[v])
dfs(v);
}
stk.push(u);
}
void dfs1(int u){
vis[u] = 1;
components[u] = numberOfComponents;
for(auto v : adjReverse[u]){
if(!vis[v])
dfs1(v);
}
}
void scc(){
memset(vis, false, sizeof vis);
while(!stk.empty()){
int ele = stk.top();
stk.pop();
if(!vis[ele]){
numberOfComponents++;
dfs1(ele);
}
}
}
int main(){
init();
for(int i = 0; i < m; i++){
int a, b;
cin >> a >> b;
adj[a].push_back(b);
adjReverse[b].push_back(a);
}
for(int i = 1; i <= n; i++){
if(!vis[i])
dfs0(i);
}
scc();
//DAG of SCC is formed calculate indegree of components
for(int i = 1;i <= n; i++){
for(int j = 0;j < adj[i].size(); j++){
int adjacentVertex = adj[i][j];
if(components[i] != components[adjacentVertex]){
// in degree of the strongly connected component.
in_degree[components[adjacentVertex]]++;
}
}
}
}