Submission #710342

#	Time	Username	Problem	Language	Result	Execution time	Memory
710342		lam	Duathlon (APIO18_duathlon)	C++14	23 / 100	126 ms	39540 KiB

count_triplets

#include <bits/stdc++.h>
#define int long long
using namespace std;
const int maxn = 1e5 + 10;
int n,m;
vector <int> adj[maxn],adj2[maxn];
int dp[maxn],dp2[maxn];
stack <int> st;
int l[maxn],t[maxn],cnt2;
int scc, id[maxn], s[maxn];
bool dau[maxn];
vector <int> root;
int ans = 0LL;
void dfs(int x, int p)
{
    dau[x] = 1;
    dp[x] = 0;
    for (int i:adj[x])
        if (i!=p)
    {
        dfs(i,x);
        dp[x] += dp[i]+1;
    }
}

void dfs2(int x, int p, int val)
{
    dp2[x] = val;
    val++;
    vector <int> pre,suf;
    for (int i:adj[x])
        if (i!=p)
    {
        pre.push_back(dp[i]+1);
        suf.push_back(dp[i]+1);
    }
    for (int i=1; i<pre.size(); i++) pre[i]+=pre[i-1];
    for (int i=suf.size()-2; i>=0; i--) suf[i]+=suf[i+1];
    int cnt=0;
    for (int i:adj[x])
        if (i!=p)
    {
        int val2 = val;
        if (cnt>0) val2 += pre[cnt-1];
        if (cnt<(int)suf.size()-1) val2+=suf[cnt+1];
        cnt++;
        dfs2(i,x,val2);
    }
}

void dfs3(int x, int p, int sz)
{
    int val = dp2[x];
    int temp = (sz - 1 - val);
    if (temp>0&&val>0)
    ans += val*temp;
    for (int i:adj[x])
        if (i!=p)
    {
        dfs3(i,x,sz);
        val = dp[i]+1;
        temp = sz - 1 - val;
        if (temp>0&&val>0) ans+=val*temp;
    }
}

void build(int x, int p)
{
    st.push(x);
    l[x]=t[x]=++cnt2;
    for (int i:adj2[x])
        if (i!=p)
    {
        if (t[i]==0)
        {
            build(i,x);
            l[x]=min(l[x],l[i]);
        }
        else l[x]=min(l[x],t[i]);
    }
    if (l[x]==t[x])
    {
        scc++; int temp;
        do
        {
            temp = st.top(); st.pop();
            s[scc] ++ ;
            id[temp] = scc;
        }
        while (temp!=x);
    }
}

signed main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr); cout.tie(nullptr);
    cin>>n>>m;
    for (int i=1; i<=m; i++)
    {
        int u,v; cin>>u>>v;
        adj2[u].push_back(v);
        adj2[v].push_back(u);
    }
    scc=cnt2=0;
    for (int i=1; i<=n; i++) if (!t[i]) build(i,i);
    for (int i=1; i<=n; i++)
        for (int j:adj2[i])
            if (id[i]!=id[j])
                adj[id[i]].push_back(id[j]);
    n = scc;
    fill_n(dau,n+1,0);
    for (int i=1; i<=n; i++) if (!dau[i]) dfs(i,i), root.push_back(i);
    for (int i:root) dfs2(i,i,0);
    for (int i:root) dfs3(i,i,dp[i]+1);
    cout<<ans<<'\n';
}

Compilation message (stderr)

count_triplets.cpp: In function 'void dfs2(long long int, long long int, long long int)':
count_triplets.cpp:37:20: warning: comparison of integer expressions of different signedness: 'long long int' and 'std::vector<long long int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   37 |     for (int i=1; i<pre.size(); i++) pre[i]+=pre[i-1];
      |                   ~^~~~~~~~~~~

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