application of Kosaraju algorithm

#include <iostream>
#include <cstring>
#include <stack>

using namespace std;

const int M = 5e4 + 10, N = 1e4 + 10;

int e[M], ne[M], h[N], idx, sccNo[N], outdeg[N], color[N], re[M], rne[M], rh[N], curScc, ans[N];

stack<int> order;

enum COLOR {
    WHITE, GRAY, BLACK
};

void addArc(int x, int y){
    e[idx] = y;
    re[idx] = x;
    ne[idx] = h[x];
    rne[idx] = rh[y];
    h[x] = idx;
    rh[y] = idx;
    idx ++;
}

void dfs1(int u){
    color[u] = GRAY;

    for(int i = h[u]; i != -1; i = ne[i]){
        int j = e[i];
        if(color[j] == WHITE){
            dfs1(j);
        }
    }

    color[u] = BLACK;
    order.push(u);
}

void dfs2(int u){
    color[u] = GRAY;
    sccNo[u] = curScc;
    ans[curScc] ++;
    for(int i = rh[u]; i != -1; i = rne[i]){
        int j = re[i];
        if(color[j] == WHITE){
            dfs2(j);
        }
    }
    color[u] = BLACK;
}

void mark_scc(int n){
    //perform dfs on G
    for(int i = 1; i <= n; i ++){
        if(color[i] == WHITE)dfs1(i);
    }

    memset(color, 0, sizeof color);
    //perform dfs on G transpose
    while(order.size()){
        int t = order.top();
        order.pop();
        if(color[t] == WHITE){
            dfs2(t);
            curScc ++;
        }
    }
}

void construct_dag(int n){
    for(int i = 1; i <= n; i ++){
        for(int j = h[i]; j != -1; j = ne[j]){
            int k = e[j];
            if(sccNo[k] == sccNo[i])continue;
            outdeg[sccNo[i]] ++;
        }
    }
}

void solve(int n){
    mark_scc(n);

    construct_dag(n);

    int cnt = 0, res = 0;
    for(int i = 0; i < curScc; i ++){
        if(outdeg[i] == 0){
            cnt ++;
            res = ans[i];
        }
        if(cnt == 2){
            res = 0;
            break;
        }
    }

    cout << res << endl;
}

int main(){
    int n, m;
    cin >> n >> m;
    memset(h, -1, sizeof h);
    memset(rh, -1, sizeof rh);

    while(m--){
        int x, y;
        cin >> x >> y;
        addArc(x, y);
    }

    solve(n);

    return 0;
}