Submission #3597480

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Source Code Expand

#include <cstdio>
#include <iostream>
#include <algorithm>
#include <string>
#include <cstring>
#include <vector>
#include <queue>
#include <set>
#include <map>
#include <cmath>
#include <iomanip>
#include <cassert>
#include <bitset>
using namespace std;
 
typedef pair<int, int> P;
#define rep(i, n) for (int i=0; i<(n); i++)
#define all(c) (c).begin(), (c).end()
#define uniq(c) c.erase(unique(all(c)), (c).end())
#define index(xs, x) (int)(lower_bound(all(xs), x) - xs.begin())
#define _1 first
#define _2 second
#define pb push_back
#define INF 1145141919
#define MOD 1000000007
 
int N, M;
vector<P> G[100000];
int low[100000], ord[100000];
int sz[100000], sz_e[100000], leaves[100000];
bool is_bridge[150000];
void dfs(int x, int p, int r) {
  low[x] = ord[x] = r;
  for (P pp : G[x]) if (pp._1 != p) {
    int t = pp._1, e = pp._2;
    if (ord[t] != -1) {
      low[x] = min(low[x], ord[t]);
      continue;
    }
    dfs(t, x, r+1);
    low[x] = min(low[x], low[t]);
    if (low[t] > ord[x]) is_bridge[e] = true;
  }
}
void dfs2(int x, int p, int k) {
  ord[x] = k;
  for (P pp : G[x]) if (pp._1 != p) {
    int t = pp._1, e = pp._2;
    if (ord[t] != -1 || is_bridge[e]) continue;
    dfs2(t, x, k);
  }
}
void dfs3(int x, int p) {
  sz[x] = 1;
  sz_e[x] = 0;
  leaves[x] = 0;
  for (P pp : G[x]) if (pp._1 != p) {
    int t = pp._1, e = pp._2;
    dfs3(t, x);
    sz[x] += sz[t];
    sz_e[x] += e + sz_e[t];
    leaves[x] += leaves[t];
  }
  if (leaves[x] == 0) leaves[x]++;
}
 
int solve(int x, int p) {
  int m = INF;
  for (P pp : G[x]) if (pp._1 != p) {
    int t = pp._1, e = pp._2;
    m = min(m, solve(t, x));
 
    if (sz[t] == 2 && sz_e[t] == 1) continue;
    if (N-sz[t] == 2 && sz_e[0]-e-sz_e[t] == 1) continue;
    int ue_leaves = 0, sita_leaves = 0;
    if (N-sz[t] > 1) ue_leaves = (x == 0 ? 0 : G[0].size() == 1) + leaves[0] - leaves[t] + (G[x].size() <= 2);
    if (sz[t] > 1) sita_leaves = leaves[t] + (G[t].size() == 2);
    int num = (ue_leaves+1)/2 + (sita_leaves+1)/2;
    m = min(m, num);
  }
  return m;
}
 
signed main() {
  ios::sync_with_stdio(false); cin.tie(0);
  cin >> N >> M;
  vector<P> edges;
  rep(i, M) {
    int a, b;
    cin >> a >> b;
    edges.pb(P(a, b));
    G[a].pb(P(b, i));
    G[b].pb(P(a, i));
  }
  rep(i, N) ord[i] = -1;
  dfs(0, -1, 0);
  int k = 0;
  rep(i, N) ord[i] = -1;
  rep(i, N) if (ord[i] == -1) dfs2(i, -1, k++);
  rep(i, N) sz[ord[i]]++;
  rep(i, N) G[i].clear();
  N = k;
  rep(i, M) if (is_bridge[i]) {
    int a = ord[edges[i]._1], b = ord[edges[i]._2];
    G[a].pb(P(b, sz[a] == 1 && sz[b] == 1));
    G[b].pb(P(a, sz[a] == 1 && sz[b] == 1));
  }
  dfs3(0, -1);
  int m = solve(0, -1);
  if (m == INF) cout << "-1\n";
  else cout << m << "\n";
  return 0;
}

Submission Info

Judge Result