Submission #711875

#	Time	Username	Problem	Language	Result	Execution time	Memory
711875		Pety	Pipes (CEOI15_pipes)	C++14	100 / 100	3145 ms	14444 KiB

pipes

#include <vector>
#include <iostream>
#include <cassert>
 
using namespace std;
 
int n, m, x, y, sz[100002], p[100002], dp[20][100002], depth[100002];
vector<int>G[100002];
 
int find (int x) {
  if (p[x] == x)
    return x;
  return p[x] = find(p[x]);
}
 
void dfs2 (int x, int par) {
  dp[0][x] = par;
  depth[x] = depth[par] + 1;
  for (int i = 1; (1 << i) < n; i++)
    dp[i][x] = dp[i - 1][dp[i - 1][x]];
  for (auto it : G[x]) {
    if (it == par)
      continue;
    dfs2(it, x);
  }
}
int cnt;
void merge (int x, int y) {
  int px = find(x);
  int py = find(y);
  if (px == py)
    return;
 
  if (sz[px] > sz[py]) {
    swap(x, y);
    swap(px, py);
  }
  G[x].push_back(y);
  G[y].push_back(x);
 
  p[px] = py;
  sz[py] += sz[px];
  dfs2(x, y);
}
 
int lca (int x, int y) {
  if (depth[x] > depth[y])
    swap(x, y);
  int d = depth[y] - depth[x];
  for (int i = 0; (1 << i) <= d; i++)
    if (d & (1 << i))
      y = dp[i][y];
  if (x == y)
    return x;
  for (int i = 19; i >= 0; i--)
    if ((1 << i) != n && dp[i][x] != dp[i][y]) {
      x = dp[i][x];
      y = dp[i][y];
    }
  return dp[0][x];
}
 
int add[100002], viz[100002];
 
void dfs (int x, int par) {
  viz[x] = 1;
  for (auto it : G[x]) {
    if (it == par)
      continue;
    dfs(it, x);
    add[x] += add[it];
  }
  if (add[x] == 0 && par != 0)
    cout << x << " " << par << "\n";
}
 
void dfs3 (int x, pair<int, int> edge) {
  viz[x] = 1;
  int i = 0;
  for (auto it : G[x]) {
    if (edge == make_pair(x, i)) {
      i++;
      continue;
    }
    if (!viz[it])
       dfs3(it, edge);
    i++;
  }
}
 
int main () 
{
  ios_base::sync_with_stdio(false);
  cin.tie(0); cout.tie(0);
  cin >> n >> m;
  for (int i = 1; i <= n; i++) {
    p[i] = i;
    sz[i] = 1;
  }
  if (m <= 200) {
    for (int i = 1; i <= m; i++) {
      int x, y;
      cin >> x >> y;
      G[x].push_back(y);
      G[y].push_back(x);
    }
    for (int x = 1; x <=n; x++) {
      for (int j = 0; j < G[x].size(); j++) {
        int val = G[x][j];
        for (int k = 1; k <= n; k++)
          viz[k] = 0;
        dfs3(x, {x, j});
        if (!viz[val] && x < val) {
          cout << x << " " << val << "\n";
        }
      }
    }
    return 0;
  }
  for (int i = 1; i <= m; i++) {
    cin >> x >> y;
    if (find(x) == find(y)) {
      int L = lca(x, y);
      assert(L > 0);
      add[L] -= 2;
      add[x]++;
      add[y]++;
    }
    else {
      merge(x, y);
      //assert(abs(depth[x] - depth[y]) == 1);
    }
  }
  for (int i = 1; i <= n; i++)
    if (!viz[find(i)])
      dfs(find(i), 0);
  return 0;
}

Compilation message (stderr)

pipes.cpp: In function 'int main()':
pipes.cpp:108:25: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
  108 |       for (int j = 0; j < G[x].size(); j++) {
      |                       ~~^~~~~~~~~~~~~

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