Submission #1694107

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Source Code Expand

#include <bits/stdc++.h>
using namespace std;
#define GET_MACRO(_1, _2, _3, NAME, ...) NAME
#define _repl(i,a,b) for(int i=(int)(a);i<(int)(b);i++)
#define _rep(i,n) _repl(i,0,n)
#define rep(...) GET_MACRO(__VA_ARGS__, _repl, _rep)(__VA_ARGS__)
#define mp(a,b) make_pair((a),(b))
#define pb(a) push_back((a))
#define all(x) (x).begin(),(x).end()
#define uniq(x) sort(all(x)),(x).erase(unique(all(x)),end(x))
#define fi first
#define se second
#define dbg(...) _dbg(#__VA_ARGS__, __VA_ARGS__)
void _dbg(string){cout<<endl;}
template<class H,class... T> void _dbg(string s,H h,T... t){int l=s.find(',');cout<<s.substr(0,l)<<" = "<<h<<", ";_dbg(s.substr(l+1),t...);}
template<class T,class U> ostream& operator<<(ostream &o, const pair<T,U> &p){o<<"("<<p.fi<<","<<p.se<<")";return o;}
template<class T> ostream& operator<<(ostream &o, const vector<T> &v){o<<"[";for(T t:v){o<<t<<",";}o<<"]";return o;}

int n,m;
vector<pair<int,int>> g[400005]; // to, e-idx
int a[500005], b[500005];
int lft[400005];
int val[400005];
int use[500005];

bool usedImos[500005], isBridge[500005], visited[400005];
int imos[400005];
void dfsInit(int v, int from){
  visited[v] = true;
  for(auto to : g[v]) if(to.fi != from){
    if(visited[to.fi]){
      int i = to.se;
      if(usedImos[i]) continue;
      if(v == a[i]) imos[a[i]]++, imos[b[i]]--;
      else imos[a[i]]--, imos[b[i]]++;
      usedImos[i]=true;
    } else {
      dfsInit(to.fi, v);
    }
  }
}
int dfsBridge(int v){
  int ret = imos[v];
  visited[v] = true;
  for(auto to : g[v]) if(!visited[to.fi]){
    int r = dfsBridge(to.fi);
    if(r==0) isBridge[to.se] = true;
    else isBridge[to.se] = false;
    ret += r;
  }
  return ret;
}

void dfs(int v);

inline void useEdge(int e, int x){
  use[e] = x;
  lft[a[e]]--; lft[b[e]]--;
  val[a[e]] += x; val[b[e]] += x;
  if(lft[a[e]]==1) dfs(a[e]);
  if(lft[b[e]]==1) dfs(b[e]);
}

void dfs(int v){
  assert(lft[v]==1);
  pair<int,int> nxt;
  for(auto &p: g[v]) if(use[p.se]==0) nxt = p;
  useEdge(nxt.se, 2 - val[v]%2);
}

int main(){
  cin>>n>>m;
  rep(i,m){
    scanf("%d %d", a+i, b+i);
    a[i]--; b[i]--;
    g[a[i]].pb(mp(b[i],i));
    g[b[i]].pb(mp(a[i],i));
    lft[a[i]]++;
    lft[b[i]]++;
  }

  fill(visited, visited+n, false);
  fill(usedImos, usedImos+m, false);
  fill(imos, imos+n, 0);
  dfsInit(0,-1);
  fill(visited, visited+n, false);
  dfsBridge(0);

  fill(use, use+m, 0);
  rep(i,m) if(isBridge[i] && use[i]==0){
    useEdge(i, 2);
  }
  for(int i=m-1; i>=0; i--) if(use[i]==0){
    useEdge(i, 1);
  }

  // dbg(vector<int>(use, use+m));

  long ans = 0;
  const long MOD = 1000000007;
  long tmp = 2;
  rep(i,m){
    ans += tmp;
    if(use[i]==2) ans += tmp;
    tmp = tmp*2 %MOD;
  }
  cout << ans %MOD << endl;

  return 0;
}

Submission Info

Compile Error

./Main.cpp: In function ‘int main()’:
./Main.cpp:74:29: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result]
     scanf("%d %d", a+i, b+i);
                             ^

Judge Result