Submission #1087866

#	Time	Username	Problem	Language	Result	Execution time	Memory
1087866		alexander707070	Duathlon (APIO18_duathlon)	C++14	66 / 100	74 ms	27988 KiB

count_triplets

#include<bits/stdc++.h>
#define MAXN 200007
using namespace std;

long long n,m,a[MAXN],b[MAXN],k;

vector< pair<int,int> > v[MAXN];
vector<int> tree[MAXN];

long long sz[MAXN],sum[MAXN],szcomp[MAXN],ans;

bool li[MAXN],bridge[MAXN];
int dp[MAXN],low[MAXN];

long long comp[MAXN],where[MAXN];

void bcc(int x,int p,int dep,int edge){
    li[x]=true; dp[x]=low[x]=dep;

    for(int i=0;i<v[x].size();i++){
        if(!li[v[x][i].first]){
            bcc(v[x][i].first,x,dep+1,v[x][i].second);
            low[x]=min(low[x],low[v[x][i].first]);
        }else if(v[x][i].first!=p){
            low[x]=min(low[x],dp[v[x][i].first]);
        }
    }

    if(p!=0 and low[x]==dp[x]){
        bridge[edge]=true;
    }
}

void mark(int x){
    comp[k]++;
    where[x]=k;
    li[x]=true;

    for(int i=0;i<v[x].size();i++){
        if(li[v[x][i].first] or bridge[v[x][i].second])continue;
        mark(v[x][i].first);
    }
}

void dfs(int x,int p){
    sz[x]=comp[x];

    for(int i=0;i<tree[x].size();i++){
        if(tree[x][i]==p or sz[tree[x][i]]!=0)continue;
        dfs(tree[x][i],x);

        sum[x]+=sz[tree[x][i]]*(sz[tree[x][i]]-1);
        sz[x]+=sz[tree[x][i]];
    }
}

void dfs2(int x,int p,int s){
    szcomp[x]=s;

    for(int i=0;i<tree[x].size();i++){
        if(tree[x][i]==p or szcomp[tree[x][i]]!=0)continue;
        dfs2(tree[x][i],x,s);
    }

    sum[x]+=(s-sz[x])*(s-sz[x]-1);
}

queue<int> q;
bool vis[MAXN];
int par[MAXN];

void dobfs(int x){
    for(int i=1;i<=n;i++)li[i]=false;

    q.push(x); par[x]=0;
    li[x]=true;

    while(!q.empty()){
        int curr=q.front();
        q.pop();

        for(int i=0;i<v[curr].size();i++){
            if(li[v[curr][i].first] or vis[v[curr][i].first])continue;

            q.push(v[curr][i].first);
            li[v[curr][i].first]=true;
            par[v[curr][i].first]=curr;
        }
    }    
}

bool check(int x,int y,int z){
    for(int i=1;i<=n;i++)vis[i]=false;

    dobfs(x);

    if(!li[y])return false;

    int w=y;
    while(y!=x){
        y=par[y];
        vis[y]=true;
    }

    if(vis[z])return false;

    dobfs(z);

    return li[w];
}

void brute(){
    int res=0;

    for(int i=1;i<=n;i++){
        for(int f=1;f<=n;f++){
            for(int t=1;t<=n;t++){
                if(i==f or f==t or i==t)continue;

                if(check(i,f,t))res++;
            }
        }
    }

    cout<<res<<"\n";
}

int main(){

    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);

    cin>>n>>m;
    for(int i=1;i<=m;i++){
        cin>>a[i]>>b[i];
        v[a[i]].push_back({b[i],i});
        v[b[i]].push_back({a[i],i});
    }

    if(n<=50){
        brute();
        return 0;
    }

    for(int i=1;i<=n;i++){
        if(!li[i])bcc(i,0,0,0);
    }

    for(int i=1;i<=n;i++)li[i]=false;

    for(int i=1;i<=n;i++){
        if(!li[i]){
            k++; mark(i);
        }
    }

    for(int i=1;i<=m;i++){
        if(where[a[i]]==where[b[i]])continue;

        tree[where[a[i]]].push_back(where[b[i]]);
        tree[where[b[i]]].push_back(where[a[i]]);
    }

    for(int i=1;i<=k;i++){
        if(sz[i]==0){
            dfs(i,0);
            dfs2(i,0,sz[i]);
        }
    }

    for(int i=1;i<=k;i++){
        ans+=(long long) comp[i]*((szcomp[i]-1)*(szcomp[i]-2)-sum[i]);
        ans-=(long long) 2*(comp[i]-1)*(szcomp[i]-comp[i]);
    }

    for(int i=1;i<=n;i++){
        long long res=0,sq=0;

        for(int f=0;f<v[i].size();f++){
            if(where[i]==where[v[i][f].first])continue;
            
            if(sz[where[i]]>sz[where[v[i][f].first]]){
                res+=sz[where[v[i][f].first]];
                sq+=(sz[where[v[i][f].first]]-1)*sz[where[v[i][f].first]];
            }else{
                res+=(szcomp[where[i]]-sz[where[i]]);
                sq+=(szcomp[where[i]]-sz[where[i]])*(szcomp[where[i]]-sz[where[i]]-1);
            }
        }

        res=res*(res-1);
        res-=sq;

        ans-=(long long) (comp[where[i]]-1)*res;
    }

    cout<<ans<<"\n";

    return 0;
}

/**
 19 24
1 2
2 3
3 4
4 1
5 6
6 7
7 5
8 9
9 10
10 8
11 12
12 13
13 11
14 15
15 16
16 14
17 18
18 19
17 19
7 8
4 5
7 11
13 17
12 14
 */

Compilation message (stderr)

count_triplets.cpp: In function 'void bcc(int, int, int, int)':
count_triplets.cpp:20:18: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<std::pair<int, int> >::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   20 |     for(int i=0;i<v[x].size();i++){
      |                 ~^~~~~~~~~~~~
count_triplets.cpp: In function 'void mark(int)':
count_triplets.cpp:39:18: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<std::pair<int, int> >::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   39 |     for(int i=0;i<v[x].size();i++){
      |                 ~^~~~~~~~~~~~
count_triplets.cpp: In function 'void dfs(int, int)':
count_triplets.cpp:48:18: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   48 |     for(int i=0;i<tree[x].size();i++){
      |                 ~^~~~~~~~~~~~~~~
count_triplets.cpp: In function 'void dfs2(int, int, int)':
count_triplets.cpp:60:18: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   60 |     for(int i=0;i<tree[x].size();i++){
      |                 ~^~~~~~~~~~~~~~~
count_triplets.cpp: In function 'void dobfs(int)':
count_triplets.cpp:82:22: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<std::pair<int, int> >::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   82 |         for(int i=0;i<v[curr].size();i++){
      |                     ~^~~~~~~~~~~~~~~
count_triplets.cpp: In function 'int main()':
count_triplets.cpp:180:22: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<std::pair<int, int> >::size_type' {aka 'long unsigned int'} [-Wsign-compare]
  180 |         for(int f=0;f<v[i].size();f++){
      |                     ~^~~~~~~~~~~~

• Subtask 1: 0 / 5
• Subtask 2: 0 / 11
• Subtask 3: 8 / 8
• Subtask 4: 10 / 10
• Subtask 5: 13 / 13
• Subtask 6: 15 / 15
• Subtask 7: 20 / 20
• Subtask 8: 0 / 8
• Subtask 9: 0 / 10