Submission #650461

#	Time	Username	Problem	Language	Result	Execution time	Memory
650461		leroycut	Valley (BOI19_valley)	C++17	0 / 100	141 ms	39104 KiB

valley

#include <bits/stdc++.h>

using namespace std;
using ll = long long;
using ld = long double;

const int N = 1e5 + 3, S = 20;
const ll INF = 1e18;
int tin[N], tout[N], up[N][S];
bool sh[N];
ll mag[N], len[N], up_mag[N][S];
int t = 1;

struct edge{
    int v, u;
};

edge ed[N];
vector<vector<pair<int, ll>>> g;


void dfs0(int v, int p, ll l){
    if(p != -1){
        up[v][0] = p;
    }
    tin[v] = t++;
    len[v] = l;
    for(auto i : g[v]){
        if(i.first == p) continue;
        dfs0(i.first, v, l + i.second);
    }
    tout[v] = t++;
}

void cal_mag(int v, int p){
    ll mi = (sh[v] ? len[v] : INF);
    if(mi != INF) mi -= 2 * len[v];
    for(auto i : g[v]){
        if(i.first == p) continue;
        cal_mag(i.first, v);
        if(mag[i.first] != INF)
            mi = min(mi, mag[i.first] + 2 * i.second);
    }
    mag[v] = mi;
    up_mag[v][0] = mi;
}




int main() {
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);

    int n, s, q, e;
    cin >> n >> s >> q >> e;
    g.resize(n + 1);

    for(int i = 1; i <= n - 1; ++i){
        int x, y;
        ll w;
        cin >> x >> y >> w;
        ed[i] = {x, y};
        g[x].push_back({y, w});
        g[y].push_back({x, w});
    }

    for(int i = 0; i < s; ++i){
        int a;
        cin >> a;
        sh[a] = true;
    }

    dfs0(e, -1, 0);
    cal_mag(e, -1);

    for(int i = 1; i <= n; ++i){
        for(int j = 1; j < S; ++j){
            up[i][j] = up[up[i][j - 1]][j - 1];
            up_mag[i][j] = min(up_mag[i][j - 1], up_mag[up[i][j - 1]][j - 1]);
        }
    }
    
    // for(int i = 1; i <= n; ++i){
    //     cout << len[i] << " " << mag[i] << " " << i << "\n";
    // }

    for(int i = 0; i < q; ++i){
        int ro, v;
        cin >> ro >> v;
        int p, ch;
        p = ed[ro].u;
        ch = ed[ro].v;
        int l = len[v];
        if(tin[ed[i].u] > tin[ed[i].v]) swap(p, ch);
        if(tin[p] < tin[v] && tout[v] < tout[p]){
            ll ans = INF;
            // cout << v << " " << up[v][0] << "!\n";
            for(int k = S - 1; k >= 0; --k){
                int cur = up[v][k];
                if(tin[p] < tin[cur] && tout[cur] < tout[p]){
                    // cout << k << " " << v << "*\n";
                    ans = min(ans, up_mag[v][k + 1]);
                    v = cur;
                }
            }
            // cout << v << " " << mag[v] << " " << up_mag[v][0] << "\n";
            if(ans == INF){
                cout << "oo\n";
            }else{
                cout << ans + l << "\n";
            }
        }else{
            cout << "escaped\n";
        }
    }
}

• Subtask 1: 0 / 9
• Subtask 2: 0 / 27
• Subtask 3: 0 / 23
• Subtask 4: 0 / 41