Submission #937061

#	Time	Username	Problem	Language	Result	Execution time	Memory
937061		Neco_arc	Valley (BOI19_valley)	C++17	100 / 100	161 ms	53336 KiB

valley

#include <bits/stdc++.h>

#define ll long long
#define fi(i, a, b) for(int i = a; i <= b; i++)
#define fid(i, a, b) for(int i = a; i >= b; i--)
#define maxn (int) 2e5 + 7

using namespace std;

int n, m, q, spe;
ll h[maxn], amin[maxn][23], Val[maxn];
int cl[maxn], In[maxn], Out[maxn], depth[maxn], cha[maxn][23];
pair<int, int> E[maxn];
vector<pair<int, ll>> edges[maxn];

void DFS(int u, int par)
{
    static int Time = 0;
    In[u] = ++Time;

    Val[u] = cl[u] ? (-h[u]) : 1e15;
    for(pair<int, ll> x : edges[u]) if(x.first != par)
    {
        ll v = x.first, w = x.second;
        h[v] = h[u] + w, depth[v] = depth[u] + 1;
        DFS(v, u);

        Val[u] = min(Val[u], Val[v] - 2 * h[u] + 2 * h[v]);
    }

    Out[u] = Time;
}

void precalc(int u, int par)
{
    for(pair<int, ll> x : edges[u]) if(x.first != par)
    {
        ll v = x.first, w = x.second;
        amin[v][0] = Val[u], cha[v][0] = u;
        fi(i, 1, 20) {
            cha[v][i] = cha[cha[v][i - 1]][i - 1];
            amin[v][i] = min(amin[v][i - 1], amin[cha[v][i - 1]][i - 1]);
        }
        precalc(v, u);
    }
}

int main()
{

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

    cin >> n >> m >> q >> spe;

    fi(i, 1, n - 1)
    {
        int x, y, w;
        cin >> x >> y >> w;
        edges[x].push_back({y, w}), edges[y].push_back({x, w});

        E[i] = {x, y};
    }

    fi(i, 1, m) {
        int x;
        cin >> x, cl[x] = 1;
    }

    DFS(spe, 0), precalc(spe, 0);

    fi(_, 1, q) {
        int id, u, p, x;
        cin >> id >> x, tie(u, p) = E[id];
        if(In[u] > In[p]) swap(u, p);

        if(!(In[p] <= In[x] && In[x] <= Out[p])) cout << "escaped\n";
        else
        {
            ll ans = Val[x], w = h[x];
            fid(i, 20, 0) if(depth[x] - (1 << i) >= depth[p]) ans = min(ans, amin[x][i]), x = cha[x][i];

            if(ans + w >= 1e15) cout << "oo\n";
            else cout << ans + w << '\n';
        }
    }

    return 0;
}

Compilation message (stderr)

valley.cpp: In function 'void precalc(int, int)':
valley.cpp:38:25: warning: unused variable 'w' [-Wunused-variable]
   38 |         ll v = x.first, w = x.second;
      |                         ^

• Subtask 1: 9 / 9
• Subtask 2: 27 / 27
• Subtask 3: 23 / 23
• Subtask 4: 41 / 41