[BOJ] 3648 : 아이돌

#include <cstdio>
#include <stack>
#include <vector>
#include <algorithm>
using namespace std;
typedef vector<int> vi;
const int n_ = 1000*2+2;
int n, m, cnt, scc[n_], chk[n_], ans[n_];
vi gph[n_];
vector<vi> res;
stack<int> stk;
int getSCC(int now) {
   chk[now] = ++cnt;
   int ret = chk[now];
   stk.push(now);
   for (int nxt : gph[now]) {
       if (!chk[nxt]) ret = min(ret, getSCC(nxt));
       else if (!scc[nxt]) ret = min(ret, chk[nxt]);
   }
   if (ret != chk[now]) return ret;
   res.push_back(vi());
   while (1) {
       int top = stk.top();
       stk.pop();
       scc[top] = res.size();
       res[res.size() - 1].push_back(top);
       ans[top] = res.size();
       if (top == now) break;
   }
   return ret;
}

int f(int u) {
    return u>n ? u-n : u+n;
}

int main() {
    while (~scanf("%d %d", &n, &m)) {
        for (int i = 0; i < n_; i++) {
            chk[i] = scc[i] = ans[i] = 0;
            gph[i].clear();
        }
        cnt = 0;
        while (!stk.empty()) stk.pop();
        res.clear();

        while (m--) {
            int u, v;
            scanf("%d %d", &u, &v);
            if (u < 0) u = -u + n;
            if (v < 0) v = -v + n;
            if (u == 1 || v == n+1) v = u;
            if (v == 1 || u == n+1) u = v;
            gph[f(u)].push_back(v);
            gph[f(v)].push_back(u);
        }

        for (int i = 1; i <= 2*n; i++) {
            if (!chk[i]) getSCC(i);
        }

        int flag = 0;
        for (int i = 1; i <= n; i++) {
            if (ans[i] == ans[i+n]) flag = 1;
        }
        puts(flag ? "no" : "yes");
    }

    return 0;
}