Submission #1400694

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Source Code Expand

#include <algorithm>
#include <bitset>
#include <cassert>
#include <cctype>
#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <ctime>
#include <deque>
#include <functional>
#include <iomanip>
#include <iostream>
#include <list>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <utility>
#include <vector>

#define REP(i,s,n) for(int i=(int)(s);i<(int)(n);i++)

using namespace std;
typedef long long int ll;
typedef vector<int> VI;
typedef vector<ll> VL;
typedef pair<int, int> PI;

/*
 * Union-Find tree
 * header requirement: vector
 */
class UnionFind {
private:
  std::vector<int> disj;
  std::vector<int> rank;
public:
  UnionFind(int n) : disj(n), rank(n) {
    for (int i = 0; i < n; ++i) {
      disj[i] = i;
      rank[i] = 0;
    }
  }
  int root(int x) {
    if (disj[x] == x) {
      return x;
    }
    return disj[x] = root(disj[x]);
  }
  void unite(int x, int y) {
    x = root(x);
    y = root(y);
    if (x == y) {
      return;
    }
    if (rank[x] < rank[y]) {
      disj[x] = y;
    } else {
      disj[y] = x;
      if (rank[x] == rank[y]) {
	++rank[x];
      }
    }
  }
  bool is_same_set(int x, int y) {
    return root(x) == root(y);
  }
};



int main(void){
  int n, m;
  cin >> n >> m;
  vector<VI> edges(n);
  REP(i, 0, m) {
    int x, y;
    cin >> x >> y;
    x--, y--;
    edges[x].push_back(y);
    edges[y].push_back(x);
  }
  // Try all possibilities to make G a bipartite graph
  int tot = 0;
  REP(bits, 0, 1 << n) {
    // Construct
    UnionFind uf(n);
    int conn = n;
    REP(i, 0, n) {
      if ((bits & 1 << i) == 0) { continue; }
      REP(j, 0, edges[i].size()) {
	int w = edges[i][j];
	if (bits & 1 << w) { continue; }
	if (not uf.is_same_set(i, w)) {
	  uf.unite(i, w);
	  conn -= 1;
	}
      }
    }
    // Are all degrees of vertices in this subgraph >0?
    // Is this subgraph connected?
    if (conn == 1) {
      tot += 1;
    }
  }
  cout << tot / 2 << endl;
}

Submission Info

Judge Result