Submission #981433

#	Time	Username	Problem	Language	Result	Execution time	Memory
981433		phoenix0423	Duathlon (APIO18_duathlon)	C++17	10 / 100	77 ms	37972 KiB

count_triplets

#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<ll, ll> pll;
#define fastio ios::sync_with_stdio(false), cin.tie(0)
#define pb push_back
#define eb emplace_back
#define f first
#define s second
const int maxn = 2e5 + 5;
vector<int> adj[maxn], nadj[maxn];
int in[maxn], low[maxn], sq[maxn], sz[maxn], dfn = 0, cnt = 0;
int n, m, ans = 0;
stack<int> st;

void dfs(int pos){
    in[pos] = low[pos] = ++dfn;
    st.push(pos);
    for(auto x : adj[pos]){
        if(in[x]) low[pos] = min(low[pos], in[x]);
        else{
            dfs(x);
            if(low[x] >= in[pos]){
                int cur = n++;
                sq[cur] = 1, in[cur] = 1;
                while(st.top() != pos){
                    nadj[cur].pb(st.top());
                    nadj[st.top()].pb(cur);
                    st.pop();
                }
                nadj[cur].pb(pos);
                nadj[pos].pb(cur);
                int sz = nadj[cur].size();
            }
        }
    }
}

void dfs2(int pos, int prev){
    sz[pos] = 1 - sq[pos];
    for(auto x : nadj[pos]){
        if(x == prev) continue;
        dfs2(x, pos);
        sz[pos] += sz[x];
    }
}

void dfs3(int pos, int prev, int tsz){
    // cout<<"d : "<<tsz<<" "<<pos<<" "<<sz[pos]<<"\n";
    if(!sq[pos]){
        ans += (tsz - 1) * (tsz - 1);
        ans -= (tsz - sz[pos]) * (tsz - sz[pos]);
        for(auto x : nadj[pos]){
            if(x == prev) continue;
            ans -= sz[x] * sz[x];
        }
    }
    else if(nadj[pos].size() >= 3){
        int lft = tsz - sz[pos], mid = nadj[pos].size() - 2;
        ans += tsz * tsz * mid;
        ans -= lft * lft  * mid;
        for(auto x : nadj[pos]){
            if(x == prev) continue;
            ans -= sz[x] * sz[x] * mid;
        }
    }
    for(auto x : nadj[pos]){
        if(x == prev) continue;
        dfs3(x, pos, tsz);
    }
}

signed main(void){
    fastio;
    cin>>n>>m;
    for(int i = 0; i < m; i++){
        int a, b;
        cin>>a>>b;
        a--, b--;
        adj[a].pb(b);
        adj[b].pb(a);
    }
    for(int i = 0; i < n; i++){
        if(!in[i]){
            dfs(i);
            dfs2(i, -1);
            dfs3(i, -1, sz[i]);
        }
    }
    cout<<ans<<"\n";

}

Compilation message (stderr)

count_triplets.cpp: In function 'void dfs(int)':
count_triplets.cpp:33:21: warning: unused variable 'sz' [-Wunused-variable]
   33 |                 int sz = nadj[cur].size();
      |                     ^~

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