Shared code

#include <bits/stdc++.h>

#define int long long
#define fastio ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);

using namespace std;

const int N = 2e5+5;
vector<int> adj[N];
int dfn[N], low[N], scc[N], inst[N], sccid, t, ans[N];
stack<int> st;

void dfs(int u){
    dfn[u] = low[u] = ++t;
    st.push(u);
    inst[u] = 1;

    for(auto v : adj[u]){
        if(!dfn[v]){
            dfs(v);
            low[u] = min(low[u],low[v]);
        }else if(inst[v]){
            low[u] = min(low[u],dfn[v]);
        }
    }

    if(dfn[u]==low[u]){
        sccid++;
        int x;
        do{
            x = st.top();
            st.pop();
            scc[x] = sccid;
            inst[x] = 0;
        }while(x!=u);
    }
}


signed main(){
    fastio
    int n,m;
    cin >> n >> m;

    for(int i = 0;i < n;i++){
        char a,b;
        int x,y;
        cin >> a >> x >> b >> y;

        int aa,bb;
        aa = (a=='+');
        bb = (b=='+');

        adj[x+n*(aa^1)].push_back(y+n*bb);
        adj[y+n*(bb^1)].push_back(x+n*aa);
    }

    for(int i = 1;i <= m+n;i++){
        if(!dfn[i]) dfs(i);
    }

    for(int i = 1;i <= m;i++){
        if(scc[i]==scc[i+n]){
            cout << "IMPOSSIBLE\n";
            return 0;
        }
    }

    for(int i = 1;i <= m;i++){
        if(scc[i]<scc[i+n]) ans[i] = 0;
        else ans[i] = 1;
    }

    for(int i = 1;i <= m;i++) cout << (ans[i] ? "+" : "-") << " ";
}