Submission #382058

#	Time	Username	Problem	Language	Result	Execution time	Memory
382058		rocks03	Valley (BOI19_valley)	C++14	100 / 100	227 ms	51692 KiB

valley

#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define pii pair<int, int>
#define pll pair<ll, ll>
#define ff first
#define ss second
#define pb push_back
#define SZ(x) ((int)(x).size())
#define all(x) x.begin(), x.end()
#define debug(x) cout << #x << ": " << x << " "
#define nl cout << "\n"
#define rep(i, a, b) for(int i = (a); i < (b); i++)
#define per(i, a, b) for(int i = (a); i >= (b); i--)
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());

struct Edge{
    int u, w, i;
};
const int MAXN = 2e5+100;
int N, S, Q, E, shop[MAXN];
pii edge[MAXN];
vector<Edge> g[MAXN];

int timer, tin[MAXN], tou[MAXN];

const int MAXK = 20+5;
int depth[MAXN], pa[MAXK][MAXN];
bool is_shop[MAXN];
ll dist[MAXN], min_dist[MAXN], value[MAXN], answer[MAXK][MAXN];

void dfs(int v, int p){
    tin[v] = timer++;
    pa[0][v] = p;
    min_dist[v] = LLONG_MAX;
    if(is_shop[v]) min_dist[v] = dist[v];
    for(auto [u, w, i] : g[v]){
        if(u != p){
            depth[u] = depth[v] + 1;
            dist[u] = dist[v] + w;
            dfs(u, v);
            if(min_dist[u] != LLONG_MAX){
                min_dist[v] = min(min_dist[v], min_dist[u]);
            }
        }
    }
    tou[v] = timer - 1;
    value[v] = LLONG_MAX;
    if(min_dist[v] != LLONG_MAX){
        value[v] = min_dist[v] - 2 * dist[v];
    }
}

bool is_ancestor(int u, int v){
    return (tin[u] <= tin[v] && tou[v] <= tou[u]);
}

void solve(){
    cin >> N >> S >> Q >> E;
    --E;
    rep(i, 0, N - 1){
        int u, v, w;
        cin >> u >> v >> w;
        --u, --v;
        g[u].pb({v, w, i});
        g[v].pb({u, w, i});
        edge[i] = {u, v};
    }
    rep(i, 0, S){
        cin >> shop[i];
        --shop[i];
        is_shop[shop[i]] = true;
    }
    dfs(E, -1);
    rep(v, 0, N){
        if(pa[0][v] == -1){
            answer[0][v] = value[v];
        } else{
            answer[0][v] = min(value[v], value[pa[0][v]]);
        }
    }
    rep(k, 0, MAXK - 1){
        rep(i, 0, N){
            if(pa[k][i] == -1){
                pa[k + 1][i] = -1;
                answer[k + 1][i] = answer[k][i];
            } else{
                pa[k + 1][i] = pa[k][pa[k][i]];
                answer[k + 1][i] = min(answer[k][i], answer[k][pa[k][i]]);
            }
        }
    }
    rep(q, 0, Q){
        int i, x;
        cin >> i >> x;
        --i, --x;
        auto [u, v] = edge[i];
        if(is_ancestor(u, x) && is_ancestor(v, x)){
            int lca = is_ancestor(u, v) ? v : u;
            int diff = depth[x] - depth[lca];
            ll cur = dist[x];
            ll ans = LLONG_MAX;
            if(value[x] != LLONG_MAX) ans = cur + value[x];
            per(k, MAXK - 1, 0){
                if(diff >> k & 1){
                    if(answer[k][x] != LLONG_MAX)
                        ans = min(ans, cur + answer[k][x]);
                    x = pa[k][x];
                }
            }
            if(ans == LLONG_MAX){
                cout << "oo\n";
            } else{
                cout << ans << "\n";
            }
        } else{
            cout << "escaped\n";
        }
    }
}

int main(){
    ios_base::sync_with_stdio(false), cin.tie(nullptr);
    solve();
    return 0;
}

Compilation message (stderr)

valley.cpp: In function 'void dfs(int, int)':
valley.cpp:37:14: warning: structured bindings only available with '-std=c++17' or '-std=gnu++17'
   37 |     for(auto [u, w, i] : g[v]){
      |              ^
valley.cpp: In function 'void solve()':
valley.cpp:97:14: warning: structured bindings only available with '-std=c++17' or '-std=gnu++17'
   97 |         auto [u, v] = edge[i];
      |              ^

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