Submission #375523

#	Time	Username	Problem	Language	Result	Execution time	Memory
375523		ritul_kr_singh	One-Way Streets (CEOI17_oneway)	C++17	100 / 100	147 ms	22248 KiB

oneway

#include <bits/stdc++.h>
using namespace std;
//#define int long long
#define sp << " " <<
#define nl << "\n"

vector<vector<pair<int, int>>> g0, g1;

vector<int> id, low, dfsNum, st;
int dfsTimer = 1;

void tarjan(int u, int parentEdge){
    dfsNum[u] = low[u] = dfsTimer++;
    st.push_back(u);
    for(auto e : g0[u]){
        if(e.second==parentEdge) continue;
        if(!dfsNum[e.first]) tarjan(e.first, e.second);
        low[u] = min(low[u], low[e.first]);
    }

    if(low[u]==dfsNum[u]){
        int v = -1;
        while(v!=u){
            v = st.back(); st.pop_back();
            id[v] = u;
        }
    }
}


int ans[100000] = {}, dir[100000] = {};
pair<int, int> edges[100000];

void dfs(int u){
    dfsNum[u] = -1;
    for(auto e : g1[u]){
        int v = e.first;
        if(dfsNum[v]<0) continue;
        dfs(v);
        dir[u] += dir[v];
        if(dir[v]==0) continue;
        if(dir[v]>0 == (id[edges[e.second].first]==u)) ans[e.second] = -1;
        else ans[e.second] = 1;
    }
}

signed main(){
    ios_base::sync_with_stdio(false); cin.tie(nullptr);
    int n, m; cin >> n >> m;

    g0.resize(n), g1.resize(n);
    for(int i=0; i<m; ++i){
        cin >> edges[i].first >> edges[i].second;
        --edges[i].first, --edges[i].second;
        if(edges[i].first == edges[i].second) continue;
        g0[edges[i].first].emplace_back(edges[i].second, i);
        g0[edges[i].second].emplace_back(edges[i].first, i);
    }
    dfsNum.assign(n, 0), id.assign(n, -1), low.resize(n);
    for(int i=0; i<n; ++i) if(!dfsNum[i]) tarjan(i, -1);

    for(int i=0; i<m; ++i){
        int x = id[edges[i].first], y = id[edges[i].second];
        if(x==y) continue;
        g1[x].emplace_back(y, i);
        g1[y].emplace_back(x, i);
    }

    int p; cin >> p;
    while(p--){
        int x, y; cin >> x >> y;
        x = id[x-1], y = id[y-1];
        ++dir[x]; // up
        --dir[y]; // down
    }

    for(int i=0; i<n; ++i) if(dfsNum[i]>=0) dfs(i);

    for(int i=0; i<m; ++i){
        char c = 'B';
        if(ans[i]<0) c = 'L';
        if(ans[i]>0) c = 'R';
        cout << c;
    }
}

Compilation message (stderr)

oneway.cpp: In function 'void dfs(int)':
oneway.cpp:42:18: warning: suggest parentheses around comparison in operand of '==' [-Wparentheses]
   42 |         if(dir[v]>0 == (id[edges[e.second].first]==u)) ans[e.second] = -1;
      |            ~~~~~~^~

• Subtask 1: 30 / 30
• Subtask 2: 30 / 30
• Subtask 3: 40 / 40