Submission #1077720

#	Time	Username	Problem	Language	Result	Execution time	Memory
1077720		hung_nm	Pipes (BOI13_pipes)	C++17	65 / 100	113 ms	50812 KiB

pipes

#include <bits/stdc++.h>
#define pb push_back
#define fi first
#define se second
#define pii pair<int, int>
#define pipii pair<int, pair<int, int>>
#define vi vector<int>
#define vpi vector<pair<int, int>>
#define inp(name) if(fopen(name, "r")) freopen(name, "r", stdin);
#define out(name) if(fopen(name, "w")) freopen(name, "w", stdout);
#define int long long
const int N = 1e6 + 5;
const int mod = 1e9 + 7;
using namespace std;
long long n, m, c[N], ans[N];
vpi ad[N];
void dfs(int u, int p, int id = 0)
{
    long long res = 0;
    for(auto [v, pos] : ad[u])
    {
        if(v == p) continue ;
        dfs(v, u, pos);
        res += ans[pos];
    }
    ans[id] = c[u] - res;
}

void sub1()
{
    dfs(1, 0);
    for(int i = 1; i <= m; ++i)
    {
        cout << 2*ans[i] << "\n";
    }
}

long long del[N], deg[N], ok[N], tmp, x, root, vis[N];
queue<int> q;

void dfs2(int u, int p, int dau)
{
    tmp += dau * c[u];
    ok[u] = 1;
    for(auto [v, i] : ad[u])
    {
        if(v == p or del[v]) continue ;
        if(ok[v] == 0)
        {
            dfs2(v, u, dau * (-1));
        }
        else
        {
            ans[x] = tmp;
            root = v;
            vis[u] = 1;
            break ;
        }
    }
}

void dfs3(int u = root, int p = root, int pos = x)
{
    vis[u] = 1;
    for(auto [v, i] : ad[u])
    {
        if(v == p or del[v] or vis[v]) continue ;
        ans[i] = 2*c[u] - ans[pos];
        dfs3(v, u, i);
    }
}
void sub2()
{
    for(int i = 1; i <= n; ++i)
    {
        if(ad[i].size() == 1)
        {
            q.push(i);
        }
        deg[i] = ad[i].size();
    }

    if( ( n - q.size() ) % 2 == 0 )
    {
        cout << 0;
        return ;
    }

    while(!q.size())
    {
        int u = q.front(); q.pop();
        for(auto [v, i] : ad[u])
        {
            if(del[v]) continue ;
            ans[i] = 2*c[u];
            c[v] -= c[u];
            deg[v]--;
            if(deg[v] == 1)
            {
                q.push(v);
            }
        }
        del[u] = 1;
    }
    long long des;
    for(int i = 1; i <= n; ++i)
    {
        if(del[i] == 0)
        {
            des = i;
            break;
        }
    }
    dfs2(des, des, 1);
    dfs3();
    for(int i = 1; i <= m; ++i)
    {
        cout << ans[i] << "\n";
    }

}
signed main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    cout.tie(0);
    cin >> n >> m;
    for(int i = 1; i <= n; ++i)
    {
        cin >> c[i];
    }

    for(int i = 1; i <= m; ++i)
    {
        int u, v;
        cin >> u >> v;
        ad[u].pb({v, i});
        ad[v].pb({u, i});
    }
    if(m > n)
    {
        cout << 0;
        return 0;
    }

    if(m == (n-1))
    {
        sub1();
        return 0;
    }


    return 0;
}

Compilation message (stderr)

pipes.cpp: In function 'void sub2()':
pipes.cpp:114:9: warning: 'des' may be used uninitialized in this function [-Wmaybe-uninitialized]
  114 |     dfs2(des, des, 1);
      |     ~~~~^~~~~~~~~~~~~

• Subtask 1: 30 / 30
• Subtask 2: 35 / 70