Submission #617601

#	Time	Username	Problem	Language	Result	Execution time	Memory
617601		ollel	Pipes (CEOI15_pipes)	C++17	0 / 100	4344 ms	65540 KiB

pipes

#include <bits/stdc++.h>
using namespace std;

typedef vector<int> vi;
typedef vector<vi> vvi;
typedef long long ll;
typedef pair<int,int> pii;

#define pb push_back
#define rep(i,a,b) for(int i = a; i < b; i++)

int n, m;

vi depth, back_edge;
vvi adj;
vi parent;
vvi children;

vector<pii> ans;

void dfs(int x, int cf) {
  parent[x] = cf;

  for (auto y : adj[x]) {
    if (y == parent[x]) continue;
    if (depth[y] != -1) {
      back_edge[x] = min(back_edge[x], depth[y]);
      continue;
    }
    children[x].pb(y);
    back_edge[y] = depth[y] = depth[x] + 1;
    dfs(y, x);
  }
}

void dfs2(int x) {
  for (auto & y : children[x]) dfs2(y);

  for (auto & y : children[x]) back_edge[x] = min(back_edge[x], back_edge[y]);
  if (depth[x] != 0) if (back_edge[x] >= depth[x]) ans.pb({x+1, parent[x]+1});
}

int main() {
  cin >> n >> m;

  adj.resize(n); depth.assign(n,-1); back_edge.assign(n,n);
  children.resize(n); parent.assign(n,-1);

  rep(i,0,m) {
    int a, b;
    cin >> a >> b;a--;b--;
    adj[a].pb(b);
    adj[b].pb(a);
  }

  rep(i,0,n) {
    if (depth[i] != -1) continue;
    depth[i] = back_edge[i] = 0;
    dfs(i, -1);
    dfs2(i);
  }

  cout << ans.size() << endl;
  for (auto [x, y] : ans) {
    cout << x << " " << y << endl;
  }
}

• Subtask 1: 0 / 10
• Subtask 2: 0 / 10
• Subtask 3: 0 / 10
• Subtask 4: 0 / 10
• Subtask 5: 0 / 10
• Subtask 6: 0 / 10
• Subtask 7: 0 / 10
• Subtask 8: 0 / 10
• Subtask 9: 0 / 10
• Subtask 10: 0 / 10