Submission #1003593

#	Time	Username	Problem	Language	Result	Execution time	Memory
1003593		aykhn	Subtree (INOI20_subtree)	C++17	100 / 100	46 ms	22640 KiB

Main

#include <bits/stdc++.h>
 
using namespace std;
 
#define int long long
#define inf 0x3F3F3F3F3F3F3F3F
 
const int MXN = 1e5 + 5;
const int LOG = 20;
const int mod = 1e9 + 7;

vector<int> adj[MXN];
int p[MXN], used[MXN], down[MXN];
int in[MXN];
int dp[MXN];

void dfs(int a)
{
  dp[a] = 0;
  used[a] = 1;
  for (int &v : adj[a])
  {
    if (!used[v]) 
    {
      p[v] = a;
      dfs(v);
    }
    else if (v != p[a]) 
    {
      assert(!down[v]);
      down[v] = a;
    }
  }
  if (down[a])
  {
    vector<int> path;
    int x = down[a];
    while (x)
    {
      path.push_back(x);
      in[x] = 1;
      if (x == a) break;
      x = p[x];
    }
    reverse(path.begin(), path.end());
    vector<int> sum(path.size(), 0);
    int co = 1;
    for (int i = (int)path.size() - 1; i >= 0; i--)
    {
      if (i == (int)path.size() - 1) co = (co * dp[path[i]]) % mod;
      else
      {
        for (int &v : adj[path[i]]) 
        {
          if (!in[v] && v != p[path[i]]) co = (co * (dp[v] + 1)) % mod;
        }
      }
      sum[i] = ((i + 1 < path.size() ? sum[i + 1] : 0) + co) % mod;
    }
    co = 1;
    for (int i = 0; i + 1 < path.size(); i++)
    {
      for (int &v : adj[path[i]])
      {
        if (!in[v] && v != p[path[i]]) 
        {
          co = (co * (dp[v] + 1)) % mod;
        }
      }
      dp[a] = (dp[a] + co) % mod;
      if (i + 2 < path.size()) dp[a] = (dp[a] + ((sum[i + 2] * co) % mod)) % mod;
    }
    for (int x : path) in[x] = 0;
  }
  else
  {
    dp[a] = 1;
    for (int &v : adj[a])
    {
      dp[a] = (dp[a] * (dp[v] + 1)) % mod;
    }
  }
}

signed main()
{
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  int n, m;
  cin >> n >> m;
  for (int i = 1; i <= m; i++)
  {
    int u, v;
    cin >> u >> v;
    adj[u].push_back(v);
    adj[v].push_back(u);
  }
  dfs(1);
  int res = 0;
  for (int i = 1; i <= n; i++)
  {
    res = (res + dp[i]) % mod;
  }
  cout << res << '\n';
}

Compilation message (stderr)

Main.cpp: In function 'void dfs(long long int)':
Main.cpp:58:24: warning: comparison of integer expressions of different signedness: 'long long int' and 'std::vector<long long int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   58 |       sum[i] = ((i + 1 < path.size() ? sum[i + 1] : 0) + co) % mod;
      |                  ~~~~~~^~~~~~~~~~~~~
Main.cpp:61:27: warning: comparison of integer expressions of different signedness: 'long long int' and 'std::vector<long long int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   61 |     for (int i = 0; i + 1 < path.size(); i++)
      |                     ~~~~~~^~~~~~~~~~~~~
Main.cpp:71:17: warning: comparison of integer expressions of different signedness: 'long long int' and 'std::vector<long long int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   71 |       if (i + 2 < path.size()) dp[a] = (dp[a] + ((sum[i + 2] * co) % mod)) % mod;
      |           ~~~~~~^~~~~~~~~~~~~

• Subtask 1: 8 / 8
• Subtask 2: 12 / 12
• Subtask 3: 30 / 30
• Subtask 4: 50 / 50