Submission #939968

#	Time	Username	Problem	Language	Result	Execution time	Memory
939968		12345678	Usmjeri (COCI17_usmjeri)	C++17	28 / 140	340 ms	89368 KiB

usmjeri

#include <bits/stdc++.h>

using namespace std;

const int nx=3e5+5, kx=19, mod=1e9+7;

int n, m, u, v, lvl[nx], pa[nx][kx], a, b, dp[nx], vs[nx], c[nx], cnt, f, res=1;
vector<int> d[nx];
vector<pair<int, int>> t[nx];

void dfs(int u, int p)
{
    lvl[u]=lvl[p]+1;
    pa[u][0]=p;
    for (int i=1; i<kx; i++) pa[u][i]=pa[pa[u][i-1]][i-1];
    for (auto v:d[u]) if (v!=p) dfs(v, u);
}

int lca(int u, int v)
{
    if (lvl[u]>lvl[v]) swap(u, v);
    for (int i=kx-1; i>=0; i--) if (lvl[pa[v][i]]>=lvl[u]) v=pa[v][i];
    if (u==v) return u;
    for (int i=kx-1; i>=0; i--) if (pa[u][i]!=pa[v][i]) u=pa[u][i], v=pa[v][i];
    return pa[u][0];
}

void dfs2(int u, int p)
{
    for (auto v:d[u]) if (v!=p) dfs2(v, u), dp[u]+=dp[v];
    if (dp[u]!=0) 
    {
        for (auto v:d[u]) if (v!=p&&dp[v]!=0) t[v].push_back({u, 0}), t[u].push_back({v, 0}); //cout<<"edge "<<u<<' '<<v<<'\n';
    }
}

void dfs3(int u)
{
    vs[u]=1;
    for (auto [v, s]:t[u])
    {
        if (!vs[v]) c[v]=(s==0)?c[u]:(1-c[u]), dfs3(v);
        else
        {
            if ((s==0&&c[v]!=c[u])||(s==1&&c[v]==c[u])) f=1;
        }
    }
}

int main()
{
    cin.tie(NULL)->sync_with_stdio(false);
    cin>>n>>m;
    for (int i=1; i<n; i++) cin>>u>>v, d[u].push_back(v), d[v].push_back(u);
    dfs(1, 1);
    for (int i=1; i<=m; i++) 
    {
        cin>>a>>b;
        int l=lca(a, b);
        dp[a]++;
        dp[b]++;
        dp[l]-=2;
        //cout<<"lca "<<a<<' '<<b<<' '<<l<<'\n';
        if (l!=a&&l!=b) t[a].push_back({b, 1}), t[b].push_back({a, 1});
    }
    if (n==1) return cout<<1, 0<<'\n';
    dfs2(1, 1);
    for (int i=2; i<=n; i++)
    {
        if (vs[i]) continue;
        //cout<<"root "<<i<<'\n';
        cnt++;
        c[i]=0;
        dfs3(i);
        if (f) return cout<<0, 0;
    }
    for (int i=1; i<=cnt; i++) res=(res*2)%mod;
    cout<<res;
}

/*
5 3
1 2
2 3
2 4
4 5
1 3
1 5
5 3

5 2
1 2
2 3
2 4
4 5
1 3
1 5
*/

• Subtask 1: 14 / 14
• Subtask 2: 14 / 14
• Subtask 3: 0 / 14
• Subtask 4: 0 / 14
• Subtask 5: 0 / 14
• Subtask 6: 0 / 14
• Subtask 7: 0 / 14
• Subtask 8: 0 / 14
• Subtask 9: 0 / 14
• Subtask 10: 0 / 14