Submission #780164

#	Time	Username	Problem	Language	Result	Execution time	Memory
780164		cig32	Logičari (COCI21_logicari)	C++17	110 / 110	142 ms	72916 KiB

Main

#include "bits/stdc++.h"
using namespace std;
#define int long long
const int MAXN = 1e6 + 10;
const int MOD = 998244353;
mt19937_64 rng((int)std::chrono::steady_clock::now().time_since_epoch().count());
int rnd(int x, int y) {
  int u = uniform_int_distribution<int>(x, y)(rng); return u;
}
int bm(int b, int p) {
  if(p==0) return 1 % MOD;
  int r = bm(b, p >> 1);
  if(p&1) return (((r*r) % MOD) * b) % MOD;
  return (r*r) % MOD;
}
int inv(int b) { 
  return bm(b, MOD-2);
}
int fastlog(int x) {
  return (x == 0 ? -1 : 64 - __builtin_clzll(x) - 1);
}
void printcase(int i) { cout << "Case #" << i << ": "; }
int n;
vector<int> adj[MAXN];
vector<int> cycle;
vector<int> dhs[MAXN];
bool vis[MAXN];
int par[MAXN];
int dep[MAXN];
void dfs0(int node, int prv) {
  vis[node] = 1;
  dep[node] = (prv == -1 ? 0 : dep[prv] + 1);
  par[node] = prv;
  for(int x: dhs[node]) {
    if(!vis[x]) {
      dfs0(x, node);
    }
    else if(x != prv && prv != -1) {
      cycle.clear();
      int u = node, v = x;
      if(dep[u] > dep[v]) swap(u, v);
      while(u != v) {
        cycle.push_back(v);
        v = par[v];
      }
      cycle.push_back(u);
    }
  }
}
bool constraint[MAXN];//must be white
int dp[MAXN][2][2];
void dfs(int node, int prv) {
  vector<int>child;
  for(int x: adj[node]) {
    if(x != prv) {
      dfs(x, node);
      child.push_back(x);
    }
  }
  // dp[node][0][0]
  dp[node][0][0]=0;
  for(int x:child)dp[node][0][0]+=dp[x][0][1];
  dp[node][0][0]=min(dp[node][0][0],(int)(1e9));
  // dp[node][0][1]
  int sm=0;
  for(int x:child)sm+=dp[x][0][1];
  dp[node][0][1]=1e9;
  for(int x:child){
    int nw=sm-dp[x][0][1]+dp[x][1][1];
    dp[node][0][1]=min(dp[node][0][1],nw);
  }
  // dp[node][1][0]
  dp[node][1][0]=1;
  for(int x:child)dp[node][1][0]+=dp[x][0][0];
  dp[node][1][0]=min(dp[node][1][0],(int)(1e9));
  // dp[node][1][1]
  sm=0;
  for(int x:child)sm+=dp[x][0][0];
  dp[node][1][1]=1e9;
  for(int x:child){
    int nw=sm-dp[x][0][0]+dp[x][1][0];
    dp[node][1][1]=min(dp[node][1][1],nw+1);
  }
  if(constraint[node]==1) dp[node][1][0]=dp[node][1][1]=1e9;
}
void solve(int tc){
  cin >> n;
  vector<pair<int,int>>edges;
  for(int i=1; i<=n; i++) {
    int u, v;
    cin >> u >> v;
    edges.push_back({u,v});
    dhs[u].push_back(v);
    dhs[v].push_back(u);
  }
  dfs0(1, -1);
  vector<pair<int,int>>banned;
  int len=cycle.size();
  for(int i=0;i<min(len,4ll);i++) banned.push_back({cycle[i],cycle[(i+1)%len]});
  int ans = 1e9;
  for(pair<int,int>x:banned){
    for(int i=1; i<=n; i++) {
      constraint[i] = 0;
      adj[i].clear();
      for(int j=0; j<2; j++) {
        for(int k=0; k<2; k++) {
          dp[i][j][k] = 1e9;
        }
      }
    }
    constraint[x.first] = constraint[x.second] = 1;
    pair<int,int>alt=x;
    swap(alt.first,alt.second);
    for(pair<int,int>y:edges){
      if(x==y || alt==y) continue;
      adj[y.first].push_back(y.second);
      adj[y.second].push_back(y.first);
    }
    dfs(1, -1);
    ans = min(ans, dp[1][0][1]);
    ans = min(ans, dp[1][1][1]);
  }
  cout << (ans == 1e9 ? -1 : ans) << '\n';
  
}
int32_t main() {
  ios::sync_with_stdio(0); cin.tie(0);
  int t = 1; //cin >> t;
  for(int i=1; i<=t; i++) solve(i);
}
// 勿忘初衷

• Subtask 1: 10 / 10
• Subtask 2: 10 / 10
• Subtask 3: 40 / 40
• Subtask 4: 50 / 50