Submission #916705

#	Time	Username	Problem	Language	Result	Execution time	Memory
916705		a_l_i_r_e_z_a	Valley (BOI19_valley)	C++17	100 / 100	167 ms	48024 KiB

valley

// In the name of God
// Hope is last to die

#include <bits/stdc++.h>
using namespace std;

typedef long long ll;
typedef long double ld;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;

#define pb push_back
#define int long long
#define S second
#define F first
#define mp make_pair
#define smax(x, y) (x) = max((x), (y))
#define smin(x, y) (x) = min((x), (y))
#define all(x) (x).begin(), (x).end()
#define len(x) ((int)(x).size())

const int maxn = 1e5 + 5, lg = 20;
const int inf = 1e18 + 7;
int n, s, q, r, timer, h[maxn], val[maxn], dp[maxn][lg], par[maxn][lg];
int ras[maxn], in[maxn], out[maxn];
vector<pair<int, pii>> adj[maxn];
bool mark[maxn];

void dfs(int v, int p){
    in[v] = timer++;
    par[v][0] = p;
    val[v] = inf;
    if(mark[v]) val[v] = h[v];
    for(auto [u, e]: adj[v]){
        if(u != p){
            h[u] = h[v] + e.F;
            ras[e.S] = u;
            dfs(u, v);
            smin(val[v], val[u]);
        }
    }
    dp[v][0] = val[v] - 2 * h[v];
    out[v] = timer;
}

bool is_par(int u, int v){
    return in[u] <= in[v] && out[u] >= out[v];
}

int32_t main()
{
    ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
    
    cin >> n >> s >> q >> r;
    for(int i = 1; i < n; i++){
        int u, v, w; cin >> u >> v >> w;
        adj[u].pb(mp(v, mp(w, i)));
        adj[v].pb(mp(u, mp(w, i)));
    }
    for(int i = 0; i < s; i++){
        int u; cin >> u; 
        mark[u] = 1;
    }
    dfs(r, r);
    for(int i = 0; i < lg; i++) dp[0][i] = inf;
    for(int b = 1; b < lg; b++){
        for(int i = 1; i <= n; i++){
            par[i][b] = par[par[i][b - 1]][b - 1];
            dp[i][b] = dp[i][b - 1];
            smin(dp[i][b], dp[par[i][b - 1]][b - 1]); 
        }
    }
    while(q--){
        int ind, v; cin >> ind >> v;
        int u = ras[ind];
        if(!is_par(u, v)) cout << "escaped\n";
        else{
            int x = v;
            int ans = dp[u][0];
            for(int b = lg - 1; b >= 0; b--){
                if(!is_par(par[v][b], u)){
                    smin(ans, dp[v][b]);
                    v = par[v][b];
                }
            }
            smin(ans, dp[v][0]);
            ans += h[x];
            if(ans <= 1e15) cout << ans << '\n';
            else cout << "oo\n";
        }
    }

    return 0;
}

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