Submission #958284

#	Time	Username	Problem	Language	Result	Execution time	Memory
958284		danikoynov	One-Way Streets (CEOI17_oneway)	C++14	0 / 100	2 ms	7768 KiB

oneway

#include<bits/stdc++.h>
#define endl '\n'

using namespace std;
typedef long long ll;

void speed()
{
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    cout.tie(NULL);
}

const int maxn = 1e5 + 10;

struct edge
{
    int v, u;

    edge(int _v = 0, int _u = 0)
    {
        v = _v;
        u = _u;
    }
} edges[maxn];

int n, m, p;
pair < int, int > road[maxn];
vector < pair < int, int > > adj[maxn];
void input()
{
    cin >> n >> m;
    for (int i = 1; i <= m; i ++)
    {
        int v, u;
        cin >> v >> u;
        adj[v].push_back({u, i});
        adj[u].push_back({v, i});
        edges[i] = edge(v, u);
    }
    cin >> p;
    for (int i = 1; i <= p; i ++)
    {
        cin >> road[i].first >> road[i].second;
    }
}

int tin[maxn], low[maxn], timer;
int bridge[maxn];
void find_bridges(int v, int id)
{
    tin[v] = low[v] = ++ timer;
    for (pair < int, int > neib : adj[v])
    {
        int u = neib.first;
        if (neib.second == id)
            continue;
        if (tin[u] != 0)
        {
            low[v] = min(low[v], tin[u]);
        }
        else
        {
            find_bridges(u, neib.second);
            if (low[u] > tin[v])
            {
                ///cout << "bridge " << v << " " << u << endl;
                bridge[neib.second] = 1;
            }
            low[v] = min(low[v], low[u]);
        }
    }
}

int cp_cnt;
int used[maxn];

vector < pair < int, int > > graph[maxn];

void trav(int v)
{
    used[v] = cp_cnt;
    for (pair < int, int > nb : adj[v])
    {
        if (bridge[nb.second])
            continue;
        if (used[nb.first])
            continue;
        trav(nb.first);
    }
}
void condense_graph()
{
    for (int i = 1; i <= n; i ++)
    {
        if (!used[i])
        {
            cp_cnt ++;
            trav(i);
        }
    }

    for (int i = 1; i <= m; i ++)
    {
        if (bridge[i])
        {
            ///cout << "edge " << used[edges[i].v] << " " << used[edges[i].u] << endl;
            graph[used[edges[i].v]].push_back({used[edges[i].u], i});
            graph[used[edges[i].u]].push_back({used[edges[i].v], i});
        }
    }

}

int way[maxn];

bool dfs(int v, int p, int target)
{
    if (v == target)
        return true;

    for (pair < int, int > nb : graph[v])
    {

        int u = nb.first, id = nb.second;
        if (u == p)
            continue;
        if (dfs(u, v, target))
        {
            ///cout << "id " << id << " " << v << " " << target << endl;
            if (used[edges[id].v] == v)
            {
                assert(way[id] != -1);
                way[id] = 1;
            }
            else
            {
                assert(way[id] != 1);
                way[id] = -1;
            }
            return true;
        }
    }
    return false;
}

void orient_edges()
{

    for (int i = 1; i <= p; i ++)
    {
        dfs(used[road[i].first], -1, used[road[i].second]);

    }

    for (int i = 1; i <= m; i ++)
    {
        if (way[i] == -1)
            cout << 'L';
        else
        if (way[i] == 1)
            cout << 'R';
        else
            cout << 'B';
    }
    cout << endl;
}
void solve()
{
    input();
    find_bridges(1, -1);

    condense_graph();
    orient_edges();
}

int main()
{
    freopen("test.txt", "r", stdin);
    ///speed();
    int t = 1;
    ///cin >> t;
    while(t --)
        solve();
    return 0;
}
/**
10 13
1 2
2 3
2 5
2 6
5 6
5 4
6 7
5 7
5 4
7 8
8 9
8 10
9 10
1
3 9
*/

Compilation message (stderr)

oneway.cpp: In function 'int main()':
oneway.cpp:179:12: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
  179 |     freopen("test.txt", "r", stdin);
      |     ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~

• Subtask 1: 0 / 30
• Subtask 2: 0 / 30
• Subtask 3: 0 / 40